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What Is Cardiac MRI?

Magnetic resonance imaging (MRI) is a safe, noninvasive test that creates detailed pictures of your organs and tissues. "Noninvasive" means that no surgery is done and no instruments are inserted into your body.

MRI uses radio waves, magnets, and a computer to create pictures of your organs and tissues. Unlike other imaging tests, MRI doesn't use ionizing radiation or carry any risk of causing cancer.

Cardiac MRI creates both still and moving pictures of your heart and major blood vessels. Doctors use cardiac MRI to get pictures of the beating heart and to look at its structure and function. These pictures can help them decide the best way to treat people who have heart problems.

Cardiac MRI is a common test. It's used to diagnose and assess many diseases and conditions, including:

Cardiac MRI can help explain results from other tests, such as x rays and computed tomography (to-MOG-rah-fee) scans (also called CT scans).

Doctors sometimes use cardiac MRI instead of invasive procedures or tests that involve radiation (such as x rays) or dyes containing iodine (these dyes may be harmful to people who have kidney problems).

A contrast agent, such as gadolinium (gad-oh-LIN-e-um), might be injected into a vein during cardiac MRI. The substance travels to the heart and highlights the heart and blood vessels on the MRI pictures. This contrast agent often is used for people who are allergic to the dyes used in CT scanning.

People who have severe kidney or liver problems may not be able to have the contrast agent. As a result, they may have a noncontrast MRI (an MRI that does not involve contrast agent).

Other Names for Cardiac MRI

  • Heart MRI
  • Cardiovascular MRI
  • Cardiac nuclear magnetic resonance (NMR)

What To Expect Before Cardiac MRI

You'll be asked to fill out a screening form before having cardiac MRI. The form may ask whether you've had any previous surgeries. It also may ask whether you have any metal objects or medical devices (like a cardiac pacemaker) in your body.

Some implanted medical devices, such as man-made heart valves and coronary stents, are safe around the MRI machine, but others are not. For example, the MRI machine can:

  • Cause implanted cardiac pacemakers and defibrillators to malfunction.
  • Damage cochlear (inner-ear) implants. Cochlear implants are small, electronic devices that help people who are deaf or who can't hear well understand speech and the sounds around them.
  • Cause brain aneurysm (AN-u-rism) clips to move as a result of the MRI's strong magnetic field. This can cause severe injury.

Talk to your doctor or the MRI technician if you have concerns about any implanted devices that may interfere with the MRI. 

Your doctor will let you know if you shouldn't have a cardiac MRI because of a medical device. If so, consider wearing a medical ID bracelet or necklace or carrying a medical alert card that states that you shouldn't have an MRI.

If you're pregnant, make sure your doctor knows before you have an MRI. No harmful effects of MRI during pregnancy have been reported; however, more research on the safety of MRI during pregnancy is needed.

Your doctor or technician will tell you whether you need to change into a hospital gown for the test. Don't bring hearing aids, credit cards, jewelry and watches, eyeglasses, pens, removable dental work, or anything that's magnetic near the MRI machine.

Tell your doctor if being in a fairly tight or confined space causes you anxiety or fear. If so, your doctor might give you medicine to help you relax. Your doctor may ask you to fast (not eat) for 6 hours before you take this medicine on the day of the test.

Some newer cardiac MRI machines are open on all sides. If you're fearful in tight or confined spaces, ask your doctor to help you find a facility that has an open MRI machine.

Your doctor will let you know whether you need to arrange for a ride home after the test.

What To Expect During Cardiac MRI

Cardiac MRI takes place in a hospital or medical imaging facility. A radiologist or other doctor who has special training in medical imaging oversees MRI testing.

Cardiac MRI usually takes 30 to 90 minutes, depending on how many pictures are needed. The test may take less time with some newer MRI machines.

The MRI machine will be located in a special room that prevents radio waves from disrupting the machine. It also prevents the MRI machine's strong magnetic fields from disrupting other equipment.

Traditional MRI machines look like long, narrow tunnels. Newer MRI machines (called short-bore systems) are shorter, wider, and don't completely surround you. Some newer machines are open on all sides. Your doctor will help decide which type of machine is best for you.

Cardiac MRI is painless and harmless. You'll lie on your back on a sliding table that goes inside the tunnel-like machine.

The MRI technician will control the machine from the next room. He or she will be able to see you through a glass window and talk to you through a speaker. Tell the technician if you have a hearing problem.

A Patient Having Cardiac MRI

The photo shows a patient lying on a sliding table outside of a cardiac MRI machine. The table will slide into the machine, and the patient will lie quietly while the machine creates pictures of the heart.

The photo shows a patient lying on a sliding table outside of a cardiac MRI machine. The table will slide into the machine, and the patient will lie quietly while the machine creates pictures of the heart.

The MRI machine makes loud humming, tapping, and buzzing noises. Some facilities let you wear earplugs or listen to music during the test.

You will need to remain very still during the MRI. Any movement can blur the pictures. If you're unable to lie still, you may be given medicine to help you relax.

The technician might ask you to hold your breath for 10 to 15 seconds at a time while he or she takes pictures of your heart. Researchers are studying ways that will allow someone having a cardiac MRI to breathe freely during the exam, while achieving the same image quality.

A contrast agent, such as gadolinium, might be used to highlight your blood vessels or heart in the pictures. The substance usually is injected into a vein in your arm using a needle.

You may feel a cool sensation during the injection and discomfort when the needle is inserted. Gadolinium doesn't contain iodine, so it won't cause problems for people who are allergic to iodine.

Your cardiac MRI might include a stress test to detect blockages in your coronary arteries. If so, you'll get other medicines to increase the blood flow in your heart or to increase your heart rate.

What To Expect After Cardiac MRI

You'll be able to return to your normal routine once the cardiac MRI is done.

If you took medicine to help you relax during the test, your doctor will tell you when you can return to your normal routine. The medicine will make you sleepy, so you'll need someone to drive you home.

What Does Cardiac MRI Show?

The doctor supervising your scan will provide your doctor with the results of your cardiac MRI. Your doctor will discuss the findings with you.

Cardiac MRI can reveal various heart diseases and conditions, such as:

Cardiac MRI is a fast, accurate tool that can help diagnose a heart attack. The test does this by detecting areas of the heart that don't move normally, have poor blood supply, or are scarred.

Cardiac MRI also can show whether any of the coronary arteries are blocked. A blockage prevents your heart muscle from getting enough oxygen-rich blood, which can lead to a heart attack.

Currently, coronary angiography (an-jee-OG-rah-fee) is the most common procedure for looking at blockages in the coronary arteries. Coronary angiography is an invasive procedure that uses x rays and iodine-based dye.

Researchers have found that cardiac MRI can sometimes replace coronary angiography, avoiding the need to use x-ray radiation and iodine-based dye. This use of MRI is called MR angiography (MRA).

Echocardiography (echo) is the main test for diagnosing heart valve disease. However, your doctor also might recommend cardiac MRI to assess the severity of valve disease.

A cardiac MRI can confirm information about valve defects or provide more detailed information about heart valve disease.

This information can help your doctor plan your treatment. An MRI also might be done before heart valve surgery to help your surgeon plan for the surgery.

Cardiac MRI

Figure A shows the heart's position in the body and the location and angle of the MRI pictures shown in figure C. Figure B is a magnetic resonance angiogram, which sometimes is used instead of a standard angiogram. Figure C shows MRI pictures of a normal left ventricle (left image), a left ventricle damaged by a heart attack (middle image), and a left ventricle that isn't getting enough blood from the coronary arteries (right image).

Figure A shows the heart's position in the body and the location and angle of the MRI pictures shown in figure C. Figure B is a magnetic resonance angiogram, which sometimes is used instead of a standard angiogram. Figure C shows MRI pictures of a normal left ventricle (left image), a left ventricle damaged by a heart attack (middle image), and a left ventricle that isn't getting enough blood from the coronary arteries (right image).

Researchers are finding new ways to use cardiac MRI. In the future, cardiac MRI may replace x rays as the main way to guide invasive procedures such as cardiac catheterization (KATH-eh-ter-ih-ZA-shun).

Also, improvements in cardiac MRI will likely lead to better methods for detecting heart disease in the future.

What Are the Risks of Cardiac MRI?

The magnetic fields and radio waves used in cardiac MRI have no side effects. This method of taking pictures of organs and tissues doesn't carry a risk of causing cancer or birth defects.

Serious reactions to the contrast agent used during some MRI tests are very rare. However, side effects are possible and include the following:

  • Headache
  • Nausea (feeling sick to your stomach)
  • Dizziness
  • Changes in taste
  • Allergic reactions

Rarely, the contrast agent can harm people who have severe kidney or liver disease. The substance may cause a disease called nephrogenic (NEF-ro-JEN-ik) systemic fibrosis.

If your cardiac MRI includes a stress test, more medicines will be used during the test. These medicines may have other side effects that aren't expected during a regular MRI scan, such as:

  • Arrhythmias (ah-RITH-me-ahs), or irregular heartbeats
  • Chest pain
  • Shortness of breath
  • Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)

Clinical Trials

The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.

NHLBI-supported research has led to many advances in medical knowledge and care. For example, this research has helped look for better ways to diagnose and evaluate heart problems using methods such as cardiac MRI.

The NHLBI continues to support research on various testing methods, including cardiac MRI. For example, NHLBI-sponsored research includes studies that:

  • Use cardiac MRI to look at heart tissue and function in patients who have had heart attacks.
  • Explore new ways of using cardiac MRI to evaluate the heart and blood vessels in people who have cardiovascular disease.
  • Compare angiography results with cardiac MRI results in women who have symptoms of heart disease. The purpose of this research is to find out whether cardiac MRI is an easy and noninvasive way to detect problems with the inner layer of the heart muscle.

Much of this research depends on the willingness of volunteers to take part in clinical trials. Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions.

For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.

By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.

If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.

If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.

For more information about clinical trials related to cardiac MRI, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:

For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.

Links to Other Information About Cardiac MRI

NHLBI Resources

Non-NHLBI Resources

Clinical Trials

February 02, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.