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 of the animation. 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 event repeated over and over. A heartbeat actually is a complicated 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 mitral and tricuspid valves closing.

Each of your heartís 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 heartís atria contract (an event called atrial systole) and pump blood into the ventricles. The atria then begin to relax. Next, your heartís ventricles contract (an event called ventricular systole) and pump blood out of your heart.

Pumping Action

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

Blood without oxygen from the two vena cavae fill your heartís 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 heartís 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 artery 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 heartís left atrium through the pulmonary veins. As your heartís 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 back into the left atrium.

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.