How the Heart Works
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How the Heart Works

How the Heart Works How the Heart Beats

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Your heartbeat is the contraction of your heart to pump blood to your lungs and the rest of your body. Your heart's electrical system determines how fast your heart beats.

Your heartbeat

The contraction of the atria and ventricles makes a heartbeat. When your heart beats, it makes a “lub-DUB” sound. You may have heard this if you listened with a stethoscope or with your ear on someone's chest.

  • After your atria pump blood into the ventricles, the valves between the atria and ventricles close to prevent backflow. The “lub” is the sound of these valves closing.
  • After your ventricles contract to pump blood away from the heart, the aortic and pulmonary valves close and make the “dub” sound.

Your heart beats an average of 60 to 100 beats per minute. In that one minute, your heart pumps about five quarts of blood through your arteries, delivering a steady stream of oxygen and nutrients all over your body. Medical Animation Copyright © 2022 Nucleus Medical Media, All rights reserved.

What is a normal pulse?

Your pulse is the rate your heart beats. It is also called your heart rate. To find your pulse without a heartrate monitor or watch, gently place your index and middle fingers on the artery located on the inner wrist of either arm, below your thumb. You should feel a pulsing or tapping against your fingers.

Watch the second hand or set the timer on your stopwatch or phone and count the number of beats you feel in 30 seconds. Double that number to find out your heart rate or pulse for 1 minute.

  • At rest, a heart rate of 60 to 100 beats per minute is normal.  
  • When you exercise, your heart beats faster, and your heart rate speeds up to get more oxygen to your muscles.

Signals from your body’s nervous system and hormone from your endocrine system control how fast and hard your heart beats. These signals and hormones allow you to adapt to changes in the amount of oxygen and nutrients your body needs.

Electrical activity

Electrical signals cause muscles to contract. Your heart has a special electrical system called the cardiac conduction system. This system controls the rate and rhythm of the heartbeat.

With each heartbeat, an electrical signal travels from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The heartbeat process includes the following steps.

  • The signal begins in a group of cells, called pacemaker cells, located in the sinoatrial (SA) node in the right atrium.
  • The electrical signal travels through the atria, causing them to pump blood into the ventricles.
  • The electrical signal then moves down to a group of pacemaker cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here the signal slows down slightly, allowing the ventricles time to finish filling with blood.
  • The AV node fires another signal that travels along the walls of your ventricles, causing them to contract and pump blood out of your heart.
  • The ventricles relax, and the heartbeat process starts all over again in the SA node.

Some conditions affect the heart's electrical system. Examples are included below.

  • Arrhythmia is an irregular heart rhythm. Atrial fibrillation is one of the most common types of arrhythmia.
  • Conduction disorders can happen when electrical signals either do not generate properly, do not travel properly through the heart, or both.

Blood pressure

Your blood pressure is the force of the blood pushing against the walls of your arteries as the heart pumps blood. It is made up of two numbers: systolic and diastolic.

  • Systolic pressure is the pressure when the ventricles pump blood out of the heart. The pressure on your arteries is highest during this time.
  • Diastolic pressure is the pressure between beats, when the heart is filling with blood. The pressure on your arteries is lowest during this time.

For most adults, healthy blood pressure is usually less than 120 over 80, which is written as your systolic pressure number over your diastolic pressure number.

image of systolic and diastolic equation

High blood pressure is what happens when blood flows through blood vessels at higher-than-normal pressures.

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