Heart Contraction and Blood Flow

The animation below shows how your heart pumps blood. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how blood flows through the heart as it contracts and relaxes.

Heartbeat

Almost everyone has heard the real or recorded sound of a heartbeat. When your heart beats, it makes a "lub-DUB" sound. Between the time you hear "lub" and "DUB," blood is pumped through your heart and circulatory system.

A heartbeat may seem like a simple, repeated event, but it's a complex series of very precise and coordinated events that take place inside and around your heart.

Each side of your heart uses an inlet valve to help move blood between the atrium and ventricle. The tricuspid valve does this between the right atrium and ventricle. The mitral valve does this between the left atrium and ventricle. The "lub" is the sound of the tricuspid and mitral valves closing.

Each of your heart's ventricles has an outlet valve. The right ventricle uses the pulmonary valve to help move blood into the pulmonary arteries. The left ventricle uses the aortic valve to do the same for the aorta. The "DUB" is the sound of the aortic and pulmonary valves closing.

Each heartbeat has two basic parts: diastole (di-AS-toe-lee), or relaxation, and atrial and ventricular systole (SIS-toe-lee), or contraction.

During diastole, the atria and ventricles of your heart relax and begin to fill with blood. At the end of diastole, your heart's atria contract (atrial systole) and pump blood into the ventricles. The atria then begin to relax. Next, your heart's ventricles contract (ventricular systole) and pump blood out of your heart.

Pumping Action

Your heart uses its four valves to ensure your blood flows only in one direction. Healthy valves open and close in coordination with the pumping action of your heart's atria and ventricles.

Each valve has a set of flaps called leaflets or cusps. These seal or open the valves. This allows pumped blood to pass through the chambers and into your blood vessels without backing up or flowing backward.

Oxygen-poor blood from the vena cavae fills your heart's right atrium. The atrium contracts (atrial systole). The tricuspid valve located between the right atrium and ventricle opens for a short time and then shuts. This allows blood to enter into the right ventricle without flowing back into the right atrium.

When your heart's right ventricle fills with blood, it contracts (ventricular systole). The pulmonary valve located between your right ventricle and pulmonary artery opens and closes quickly.

This allows blood to enter into your pulmonary arteries without flowing back into the right ventricle. This is important because the right ventricle begins to refill with more blood through the tricuspid valve. Blood travels through the pulmonary arteries to your lungs to pick up oxygen.

Oxygen-rich blood returns from the lungs to your heart's left atrium through the pulmonary veins. As your heart's left atrium fills with blood, it contracts. This event also is called atrial systole.

The mitral valve located between the left atrium and left ventricle opens and closes quickly. This allows blood to pass from the left atrium into the left ventricle without flowing backward.

As the left ventricle fills with blood, it contracts. This event also is called ventricular systole. The aortic valve located between the left ventricle and aorta opens and closes quickly. This allows blood to flow into the aorta. The aorta is the main artery that carries blood from your heart to the rest of your body.

The aortic valve closes quickly to prevent blood from flowing back into the left ventricle, which is already filling up with new blood.

Taking Your Pulse

When your heart pumps blood through your arteries, it creates a pulse that you can feel on the arteries close to the skin's surface. For example, you can feel the pulse on the artery inside of your wrist, below your thumb.

You can count how many times your heart beats by taking your pulse. You will need a watch with a second hand.

To find your pulse, 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 and count the number of pulses you feel in 30 seconds. Double that number to find out your heart rate or pulse for 1 minute.

The usual resting pulse for an adult is 60 to 100 beats per minute. To find your resting pulse, count your pulse after you have been sitting or resting quietly for at least 10 minutes.