Arrhythmia

An arrhythmia (ah-RITH-me-ah) is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.

A heartbeat that is too fast is called tachycardia (TAK-ih-KAR-de-ah). A heartbeat that is too slow is called bradycardia (bray-de-KAR-de-ah).

Most arrhythmias are harmless, but some can be serious or even life threatening. During an arrhythmia, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.

Understanding the Heart's Electrical System

To understand arrhythmias, it helps to understand the heart's internal electrical system. The heart's electrical system controls the rate and rhythm of the heartbeat.

With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood.

Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the heart's upper right chamber, the right atrium (AY-tree-um). In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute.

From the SA node, the electrical signal travels through special pathways in the right and left atria. This causes the atria to contract and pump blood into the heart's two lower chambers, the ventricles (VEN-trih-kuls).

The electrical signal then moves down to a group of cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here, the signal slows down just a little, allowing the ventricles time to finish filling with blood.

The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. This pathway divides into a right bundle branch and a left bundle branch. The signal goes down these branches to the ventricles, causing them to contract and pump blood to the lungs and the rest of the body.

The ventricles then relax, and the heartbeat process starts all over again in the SA node. (For more information about the heart's electrical system, including detailed animations, go to the Health Topics How the Heart Works article.)

A problem with any part of this process can cause an arrhythmia. For example, in atrial fibrillation (A-tre-al fi-bri-LA-shun), a common type of arrhythmia, electrical signals travel through the atria in a fast and disorganized way. This causes the atria to quiver instead of contract.

Outlook

There are many types of arrhythmia. Most arrhythmias are harmless, but some are not. The outlook for a person who has an arrhythmia depends on the type and severity of the arrhythmia.

Even serious arrhythmias often can be successfully treated. Most people who have arrhythmias are able to live normal, healthy lives.

The four main types of arrhythmia are premature (extra) beats, supraventricular (SU-prah-ven-TRIK-yu-lar) arrhythmias, ventricular arrhythmias, and bradyarrhythmias (bray-de-ah-RITH-me-ahs).

Premature (Extra) Beats

Premature beats are the most common type of arrhythmia. They're harmless most of the time and often don't cause any symptoms.

When symptoms do occur, they usually feel like fluttering in the chest or a feeling of a skipped heartbeat. Most of the time, premature beats need no treatment, especially in healthy people.

Premature beats that occur in the atria (the heart's upper chambers) are called premature atrial contractions, or PACs. Premature beats that occur in the ventricles (the heart's lower chambers) are called premature ventricular contractions, or PVCs.

In most cases, premature beats happen naturally. However, some heart diseases can cause premature beats. They also can happen because of stress, too much exercise, or too much caffeine or nicotine.

Supraventricular Arrhythmias

Supraventricular arrhythmias are tachycardias (fast heart rates) that start in the atria or atrioventricular (AV) node. The AV node is a group of cells located between the atria and the ventricles.

Types of supraventricular arrhythmias include atrial fibrillation (AF), atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff-Parkinson-White (WPW) syndrome.

Atrial Fibrillation

AF is the most common type of serious arrhythmia. It involves a very fast and irregular contraction of the atria.

In AF, the heart's electrical signals don't begin in the SA node. Instead, they begin in another part of the atria or in the nearby pulmonary veins.

The signals don't travel normally. They may spread throughout the atria in a rapid, disorganized way. This causes the walls of the atria to quiver very fast (fibrillate) instead of beating normally. As a result, the atria aren't able to pump blood into the ventricles the way they should.

In AF, electrical signals can travel through the atria at a rate of more than 300 per minute. Some of these abnormal signals can travel to the ventricles, causing them to beat too fast and with an irregular rhythm. AF usually isn't life threatening, but it can be dangerous if it causes the ventricles to beat very fast.

AF has two major complications—stroke and heart failure.

In AF, blood can pool in the atria, causing blood clots to form. If a clot breaks off and travels to the brain, it can cause a stroke. Blood-thinning medicines that reduce the risk of stroke are an important part of treatment for people who have AF.

Heart failure occurs if the heart can't pump enough blood to meet the body's needs. AF can lead to heart failure because the ventricles are beating very fast and can't completely fill with blood. Thus, they may not be able to pump enough blood to the lungs and body.

Damage to the heart's electrical system causes AF. The damage most often is the result of other conditions that affect the health of the heart, such as high blood pressure, coronary heart disease, and rheumatic heart disease. Inflammation also is thought to play a role in the development of AF.

Other conditions also can lead to AF, including an overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. The risk of AF increases with age.

Sometimes AF and other supraventricular arrhythmias can occur for no obvious reason.

Atrial Flutter

Atrial flutter is similar to AF. However, the heart's electrical signals spread through the atria in a fast and regular—instead of irregular—rhythm. Atrial flutter is much less common than AF, but it has similar symptoms and complications.

Paroxysmal Supraventricular Tachycardia

PSVT is a very fast heart rate that begins and ends suddenly. PSVT occurs because of problems with the electrical connection between the atria and the ventricles.

In PSVT, electrical signals that begin in the atria and travel to the ventricles can reenter the atria, causing extra heartbeats. This type of arrhythmia usually isn't dangerous and tends to occur in young people. It can happen during vigorous physical activity.

A special type of PSVT is called Wolff-Parkinson-White syndrome. WPW syndrome is a condition in which the heart's electrical signals travel along an extra pathway from the atria to the ventricles.

This extra pathway disrupts the timing of the heart's electrical signals and can cause the ventricles to beat very fast. This type of arrhythmia can be life threatening.

Ventricular Arrhythmias

These arrhythmias start in the heart's lower chambers, the ventricles. They can be very dangerous and usually require medical care right away.

Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation (v-fib). Coronary heart disease, heart attack, a weakened heart muscle, and other problems can cause ventricular arrhythmias.

Ventricular Tachycardia

Ventricular tachycardia is a fast, regular beating of the ventricles that may last for only a few seconds or for much longer.

A few beats of ventricular tachycardia often don't cause problems. However, episodes that last for more than a few seconds can be dangerous. Ventricular tachycardia can turn into other, more serious arrhythmias, such as v-fib.

Ventricular Fibrillation

V-fib occurs if disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood to the body, sudden cardiac arrest and death can occur within a few minutes.

To prevent death, the condition must be treated right away with an electric shock to the heart called defibrillation (de-fib-rih-LA-shun).

V-fib may occur during or after a heart attack or in someone whose heart is already weak because of another condition.

Torsades de pointes (torsades) is a type of v-fib that causes a unique pattern on an EKG (electrocardiogram) test. Certain medicines or imbalanced amounts of potassium, calcium, or magnesium in the bloodstream can cause this condition.

People who have long QT syndrome are at increased risk for torsades. People who have this condition need to be careful about taking certain antibiotics, heart medicines, and over-the-counter products.

Bradyarrhythmias

Bradyarrhythmias occur if the heart rate is slower than normal. If the heart rate is too slow, not enough blood reaches the brain. This can cause you to pass out.

In adults, a heart rate slower than 60 beats per minute is considered a bradyarrhythmia. Some people normally have slow heart rates, especially people who are very physically fit. For them, a heartbeat slower than 60 beats per minute isn't dangerous and doesn't cause symptoms. But in other people, serious diseases or other conditions may cause bradyarrhythmias.

Bradyarrhythmias can be caused by:

• Heart attacks
• Conditions that harm or change the heart's electrical activity, such as an underactive thyroid gland or aging
• An imbalance of chemicals or other substances in the blood, such as potassium
• Medicines such as beta blockers, calcium channel blockers, some antiarrhythmia medicines, and digoxin

Arrhythmias in Children

Children's heart rates normally decrease as they get older. A newborn's heart beats between 95 to 160 times a minute. A 1-year-old's heart beats between 90 to 150 times a minute, and a 6- to 8-year-old's heart beats between 60 to 110 times a minute.

A baby or child's heart can beat fast or slow for many reasons. Like adults, when children are active, their hearts will beat faster. When they're sleeping, their hearts will beat slower. Their heart rates can speed up and slow down as they breathe in and out. All of these changes are normal.

Some children are born with heart defects that cause arrhythmias. In other children, arrhythmias can develop later in childhood. Doctors use the same tests to diagnose arrhythmias in children and adults.

Treatments for children who have arrhythmias include medicines, defibrillation (electric shock), surgically implanted devices that control the heartbeat, and other procedures that fix abnormal electrical signals in the heart.

• Dysrhythmia

An arrhythmia can occur if the electrical signals that control the heartbeat are delayed or blocked. This can happen if the special nerve cells that produce electrical signals don't work properly. It also can happen if the electrical signals don't travel normally through the heart.

An arrhythmia also can occur if another part of the heart starts to produce electrical signals. This adds to the signals from the special nerve cells and disrupts the normal heartbeat.

Smoking, heavy alcohol use, use of some drugs (such as cocaine or amphetamines), use of some prescription or over-the-counter medicines, or too much caffeine or nicotine can lead to arrhythmias in some people.

Strong emotional stress or anger can make the heart work harder, raise blood pressure, and release stress hormones. Sometimes these reactions can lead to arrhythmias.

A heart attack or other condition that damages the heart's electrical system also can cause arrhythmias. Examples of such conditions include high blood pressure, coronary heart disease, heart failure, an overactive or underactive thyroid gland (too much or too little thyroid hormone produced), and rheumatic heart disease.

Congenital (kon-JEN-ih-tal) heart defects can cause some arrhythmias, such as Wolff-Parkinson-White syndrome. The term "congenital” means the defect is present at birth.

Sometimes the cause of arrhythmias is unknown.

Arrhythmias are very common in older adults. Atrial fibrillation (a common type of arrhythmia that can cause problems) affects millions of people, and the number is rising.

Most serious arrhythmias affect people older than 60. This is because older adults are more likely to have heart disease and other health problems that can lead to arrhythmias.

Older adults also tend to be more sensitive to the side effects of medicines, some of which can cause arrhythmias. Some medicines used to treat arrhythmias can even cause arrhythmias as a side effect.

Some types of arrhythmia happen more often in children and young adults. Paroxysmal supraventricular tachycardia (PSVT), including Wolff-Parkinson-White syndrome, is more common in young people. PSVT is a fast heart rate that begins and ends suddenly.

Major Risk Factors

Arrhythmias are more common in people who have diseases or conditions that weaken the heart, such as:

• Heart attack
• Heart failure or cardiomyopathy, which weakens the heart and changes the way electrical signals move through the heart
• Heart tissue that's too thick or stiff or that hasn't formed normally
• Leaking or narrowed heart valves, which make the heart work too hard and can lead to heart failure
• Congenital heart defects (defects present at birth) that affect the heart's structure or function

Other conditions also can raise the risk for arrhythmias, such as:

• High blood pressure
• Infections that damage the heart muscle or the sac around the heart
• Diabetes, which increases the risk of high blood pressure and coronary heart disease
• Sleep apnea, which can stress the heart because the heart doesn't get enough oxygen
• An overactive or underactive thyroid gland (too much or too little thyroid hormone in the body)

Several other risk factors also can raise your risk for arrhythmias. Examples include heart surgery, certain drugs (such as cocaine or amphetamines), or an imbalance of chemicals or other substances (such as potassium) in the bloodstream.

Many arrhythmias cause no signs or symptoms. When signs or symptoms are present, the most common ones are:

• Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)
• A slow heartbeat
• An irregular heartbeat
• Feeling pauses between heartbeats

More serious signs and symptoms include:

• Anxiety
• Weakness, dizziness, and light-headedness
• Fainting or nearly fainting
• Sweating
• Shortness of breath
• Chest pain

Arrhythmias can be hard to diagnose, especially the types that only cause symptoms every once in a while. Doctors diagnose arrhythmias based on medical and family histories, a physical exam, and the results from tests and procedures.

Specialists Involved

Doctors who specialize in the diagnosis and treatment of heart diseases include:

• Cardiologists. These doctors diagnose and treat adults who have heart problems.
• Pediatric cardiologists. These doctors diagnose and treat babies, children, and youth who have heart problems.
• Electrophysiologists. These doctors are cardiologists or pediatric cardiologists who specialize in arrhythmias.

Medical and Family Histories

To diagnose an arrhythmia, your doctor may ask you to describe your symptoms. He or she may ask whether you feel fluttering in your chest and whether you feel dizzy or light-headed.

Your doctor also may ask whether you have other health problems, such as a history of heart disease, high blood pressure, diabetes, or thyroid problems. He or she may ask about your family's medical history, including whether anyone in your family:

• Has a history of arrhythmias
• Has ever had heart disease or high blood pressure
• Has died suddenly
• Has other illnesses or health problems

Your doctor will likely want to know what medicines you're taking, including over-the-counter medicines and supplements.

Your doctor may ask about your health habits, such as physical activity, smoking, or using alcohol or drugs (for example, cocaine). He or she also may want to know whether you've had emotional stress or anger.

Physical Exam

During a physical exam, your doctor may:

• Listen to the rate and rhythm of your heartbeat
• Listen to your heart for a heart murmur (an extra or unusual sound heard during your heartbeat)
• Check your pulse to find out how fast your heart is beating
• Check for swelling in your legs or feet, which could be a sign of an enlarged heart or heart failure
• Look for signs of other diseases, such as thyroid disease, that could be causing the problem

Diagnostic Tests and Procedures

EKG (Electrocardiogram)

An EKG is a simple, painless test that detects and records the heart's electrical activity. It's the most common test used to diagnose arrhythmias.

An EKG shows how fast the heart is beating and its rhythm (steady or irregular). It also records the strength and timing of electrical signals as they pass through the heart.

A standard EKG only records the heartbeat for a few seconds. It won't detect arrhythmias that don't happen during the test.

To diagnose arrhythmias that come and go, your doctor may have you wear a portable EKG monitor. The two most common types of portable EKGs are Holter and event monitors.

Holter and Event Monitors

A Holter monitor records the heart's electrical signals for a full 24- or 48-hour period. You wear one while you do your normal daily activities. This allows the monitor to record your heart for a longer time than a standard EKG.

An event monitor is similar to a Holter monitor. You wear an event monitor while doing your normal activities. However, an event monitor only records your heart's electrical activity at certain times while you're wearing it.

For many event monitors, you push a button to start the monitor when you feel symptoms. Other event monitors start automatically when they sense abnormal heart rhythms.

Some event monitors are able to send data about your heart's electrical activity to a central monitoring station. Technicians at the station review the information and send it to your doctor. You also can use the device to report any symptoms you're having.

You can wear an event monitor for weeks or until symptoms occur.

Other Tests

Other tests also are used to help diagnose arrhythmias.

Blood tests. Blood tests check the level of substances in the blood, such as potassium and thyroid hormone. Abnormal levels of these substances can increase your chances of having an arrhythmia.

Chest x ray. A chest x ray is a painless test that creates pictures of the structures in your chest, such as your heart and lungs. This test can show whether your heart is enlarged.

Echocardiography. This test uses sound waves to create a moving picture of your heart. Echocardiography (echo) provides information about the size and shape of your heart and how well your heart chambers and valves are working.

The test also can identify areas of poor blood flow to the heart, areas of heart muscle that aren't contracting normally, and previous injury to the heart muscle caused by poor blood flow.

There are several types of echo, including stress echo. This test is done both before and after a stress test (see below). A stress echo usually is done to find out whether you have decreased blood flow to your heart, a sign of coronary heart disease (CHD).

A transesophageal (tranz-ih-sof-uh-JEE-ul) echo, or TEE, is a special type of echo that takes pictures of the heart through the esophagus. The esophagus is the passage leading from your mouth to your stomach.

Stress test. Some heart problems are easier to diagnose when your heart is working hard and beating fast. During stress testing, you exercise to make your heart work hard and beat fast while heart tests are done. If you can't exercise, you may be given medicine to make your heart work hard and beat fast.

The heart tests done during stress testing may include nuclear heart scanning, echo, and positron emission tomography (PET) scanning of the heart.

Electrophysiology study (EPS). This test is used to assess serious arrhythmias. During an EPS, a thin, flexible wire is passed through a vein in your groin (upper thigh) or arm to your heart. The wire records your heart's electrical signals.

Your doctor can use the wire to electrically stimulate your heart and trigger an arrhythmia. This allows your doctor to see whether an antiarrhythmia medicine can stop the problem.

Catheter ablation, a procedure used to treat some arrhythmias, may be done during an EPS.

Tilt table testing. This test sometimes is used to help find the cause of fainting spells. You lie on a table that moves from a lying down to an upright position. The change in position may cause you to faint.

Your doctor watches your symptoms, heart rate, EKG reading, and blood pressure throughout the test. He or she may give you medicine and then check your response to the medicine.

Coronary angiography. Coronary angiography uses dye and special x rays to show the inside of your coronary arteries. To get the dye into your coronary arteries, your doctor will use a procedure called cardiac catheterization (KATH-e-ter-ih-ZA-shun).

A thin, flexible tube called a catheter is put into a blood vessel in your arm, groin (upper thigh), or neck. The tube is threaded into your coronary arteries, and the dye is released into your bloodstream.

Special x rays are taken while the dye is flowing through your coronary arteries. The dye lets your doctor study the flow of blood through your heart and blood vessels. This helps your doctor find blockages that can cause a heart attack.

Implantable loop recorder. This device detects abnormal heart rhythms. Minor surgery is used to place this device under the skin in the chest area.

An implantable loop recorder helps doctors figure out why a person may be having palpitations or fainting spells, especially if these symptoms don't happen very often. The device can be used for as long as 12 to 24 months.

Common arrhythmia treatments include medicines, medical procedures, and surgery. Your doctor may recommend treatment if your arrhythmia causes serious symptoms, such as dizziness, chest pain, or fainting.

Your doctor also may recommend treatment if the arrhythmia increases your risk for problems such as heart failure, stroke, or sudden cardiac arrest.

Medicines

Medicines can slow down a heart that's beating too fast. They also can change an abnormal heart rhythm to a normal, steady rhythm. Medicines that do this are called antiarrhythmics.

Some of the medicines used to slow a fast heart rate are beta blockers (such as metoprolol and atenolol), calcium channel blockers (such as diltiazem and verapamil), and digoxin (digitalis). These medicines often are used to treat atrial fibrillation (AF).

Some of the medicines used to restore a normal heart rhythm are amiodarone, sotalol, flecainide, propafenone, dofetilide, ibutilide, quinidine, procainamide, and disopyramide. These medicines often have side effects. Some side effects can make an arrhythmia worse or even cause a different kind of arrhythmia.

Currently, no medicine can reliably speed up a slow heart rate. Abnormally slow heart rates are treated with pacemakers.

People who have AF and some other arrhythmias may be treated with blood-thinning medicines. These medicines reduce the risk of blood clots forming. Warfarin (Coumadin®), dabigatran, heparin, and aspirin are examples of blood-thinning medicines.

Medicines also can control an underlying medical condition that might be causing an arrhythmia, such as heart disease or a thyroid condition.

Medical Procedures

Some arrhythmias are treated with pacemakers. A pacemaker is a small device that's placed under the skin of your chest or abdomen to help control abnormal heart rhythms.

Pacemakers have sensors that detect the heart's electrical activity. When the device senses an abnormal heart rhythm, it sends electrical pulses to prompt the heart to beat at a normal rate.

Some arrhythmias are treated with a jolt of electricity to the heart. This type of treatment is called cardioversion or defibrillation, depending on which type of arrhythmia is being treated.

Some people who are at risk for ventricular fibrillation are treated with a device called an implantable cardioverter defibrillator (ICD). Like a pacemaker, an ICD is a small device that's placed under the skin in the chest. This device uses electrical pulses or shocks to help control life-threatening arrhythmias.

An ICD continuously monitors the heartbeat. If it senses a dangerous ventricular arrhythmia, it sends an electric shock to the heart to restore a normal heartbeat.

A procedure called catheter ablation is used to treat some arrhythmias if medicines don't work. During this procedure, a thin, flexible tube is put into a blood vessel in your arm, groin (upper thigh), or neck. Then, the tube is guided to your heart.

A special machine sends energy through the tube to your heart. The energy finds and destroys small areas of heart tissue where abnormal heart rhythms may start. Catheter ablation usually is done in a hospital as part of an electrophysiology study.

Your doctor may recommend transesophageal echocardiography before catheter ablation to make sure no blood clots are present in the atria (the heart's upper chambers).

Surgery

Doctors treat some arrhythmias with surgery. This may occur if surgery is already being done for another reason, such as repair of a heart valve.

One type of surgery for AF is called maze surgery. During this surgery, a surgeon makes small cuts or burns in the atria. These cuts or burns prevent the spread of disorganized electrical signals.

If coronary heart disease is the cause of your arrhythmia, your doctor may recommend coronary artery bypass grafting. This surgery improves blood flow to the heart muscle.

Other Treatments

Vagal maneuvers are another type of treatment for arrhythmia. These simple exercises sometimes can stop or slow down certain types of supraventricular arrhythmias. They do this by affecting the vagus nerve, which helps control the heart rate.

Some vagal maneuvers include:

• Gagging
• Holding your breath and bearing down (Valsalva maneuver)
• Immersing your face in ice-cold water
• Coughing
• Putting your fingers on your eyelids and pressing down gently

Vagal maneuvers aren't an appropriate treatment for everyone. Discuss with your doctor whether vagal maneuvers are an option for you.

Many arrhythmias are harmless. It's common to have an occasional extra heartbeat or mild palpitations. People who have harmless arrhythmias can live healthy lives. They usually don't need treatment for their arrhythmias.

Even people who have serious arrhythmias often can be successfully treated and lead normal lives.

Ongoing Care

If you have an arrhythmia that requires treatment, you should:

• Keep all of your medical appointments. Bring a list of all the medicines you're taking to every doctor and emergency room visit. This will help your doctors know exactly what medicines you're taking, which can help prevent medication errors.
• Take your medicines as prescribed. Check with your doctor before taking over-the-counter medicines, nutritional supplements, or cold and allergy medicines. Some of these products can trigger rapid heart rhythms or interact poorly with heart rhythm medicines.
• Tell your doctor if you're having side effects from your medicines. Side effects might include depression and palpitations. These side effects often can be treated.
• Tell your doctor if arrhythmia symptoms are getting worse or if you have new symptoms.
• See your doctor for regular checkups if you're taking blood-thinning medicines. You may need routine blood tests to check how the medicines are working.

If you have an arrhythmia, taking care of yourself is important. If you feel dizzy or faint, you should lie down. Don't try to walk or drive. Let your doctor know about these symptoms.

Ask your doctor whether vagal maneuvers are an option for you. These exercises can help stop a rapid heartbeat, but they're not appropriate for everyone.

Learn how to take your pulse. Discuss with your doctor what pulse rate is normal for you. Keep a record of changes in your pulse rate and share this information with your doctor.

Lifestyle Changes

Many arrhythmias are caused by underlying heart disease. Keep your heart healthy by following a healthy diet.

A healthy diet includes a variety of fruits and vegetables. It also includes whole grains, fat-free or low-fat dairy products, and protein foods, such as lean meats, poultry without skin, seafood, processed soy products, nuts, seeds, and beans and peas.

A healthy diet is low in sodium (salt), added sugars, solid fats, and refined grains. Solid fats are saturated fat and trans fatty acids. Refined grains come from processing whole grains, which results in a loss of nutrients (such as dietary fiber).

For more information about following a healthy diet, go to the National Heart, Lung, and Blood Institute's "Your Guide to Lowering Your Blood Pressure With DASH" and the U.S. Department of Agriculture's ChooseMyPlate.gov Web site. Both resources provide general information about healthy eating.

A healthy lifestyle also includes being physically active, quitting smoking, maintaining a healthy weight, and keeping your blood cholesterol and blood pressure at healthy levels.

Strong emotional stress or anger can lead to arrhythmias. Try to manage stress and anger through activities such as yoga, quiet time, meditation, and relaxation techniques. Getting support from friends and family also can help you manage stress.

Your doctor may want you to avoid certain substances if they make your heart beat too fast. These substances may include alcohol and cold and cough medicines.