Your cardiovascular system is a vital, complex system made of the heart and blood vessels. Many conditions and diseases affect this system. To take care of your health it is helpful to have some basic knowledge about how the heart functions.

Your Heart and How it Works

The heart is a muscle. It is slightly larger than your fist and weighs less than a pound. The heart's job is to pump blood to the body. The heart is made of three layers. The thickest layer is called the myocardium. It is surrounded by a fiber-like bag called the pericardium. The inside of the myocardium is lined by a thin layer called the endocardium.

The Structure of the Heart

The normal heart has four chambers. A wall divides the heart into a right side and a left side. Each side of the heart is divided into two chambers. The upper chamber is called the atrium and the lower chamber is called the ventricle. These chambers are separated by valves.

Heart Valves

The heart valves act like doors, which allow blood to flow only in one direction. Valves control the flow of blood through the heart to the lungs and to the rest of the body. The types of valves are the:
  • Tricuspid valve separating your right atrium from your right ventricle.
  • Pulmonic valve separating your right ventricle from your lungs.
  • Mitral valve between your left atrium and your left ventricle.
  • Aortic valve that controls blood flow from your left ventricle to the rest of your body.

Blood Vessels

Blood vessels carry blood away from the heart and back again. Vessels that carry blood from the heart to the body are called arteries. Vessels that carry blood from the body back to the heart are called veins.

How the Heart Functions

Your heart acts as a pump with two sides. There is a right-sided pump and a left-sided pump. Blood enters the right atrium and flows into the right ventricle. The tricuspid valve prevents the blood from flowing back into the atrium. The blood then flows out of the heart to the lungs through the pulmonic valve, to pick up oxygen. The oxygen-rich blood from the lungs goes into the left atrium of the heart. Blood flows from the left atrium into the left ventricle through the mitral valve. The mitral valve prevents blood flowing back into the atrium. Then the blood flows out of the left ventricle to the rest of the body through a large artery, called the aorta. The aortic valve prevents blood from flowing back into the ventricle. As blood moves through the body, oxygen is used. Blood that has the oxygen used returns to the right side of the heart through your veins. This process occurs with each heart beat.

Blood Supply in the Heart

Your heart muscle needs a constant supply of oxygen. Oxygen is carried to your heart muscle through the coronary arteries. These coronary arteries lie on the surface of the heart itself. Two main coronary arteries, a right and a left, supply the heart muscle with blood. These divide into many smaller branches that go into the heart muscle. Blood flows through these heart arteries during the heart's resting cycle.

Your Heartbeat

Each heart beat has two phases. The resting phase is called diastole. During diastole, blood from the atria (the top chambers of the heart) fills the ventricles (the bottom chambers). Then the ventricles pump blood to your body or lungs. This pumping phase is called systole. This pumping phase is when the heart works the hardest. The work of the heart changes with your body's needs. For example, when you exercise, your body needs more blood and oxygen. Your heart pumps harder and faster to deliver more blood to the body. When you sleep, less blood and oxygen is needed and your heart slows down. With some heart conditions, the heart may not react to the body's needs. It may be less efficient at getting blood and oxygen to all parts of your body.

Normal Conduction

Your heart has a normal conduction/electrical system that stimulates the heart muscle to beat. Electrical signals travel from the upper chambers to the lower chambers through this conduction system. The yellow path of the diagram shows how the normal signals travel through the hearts conduction system to create a heartbeat.
  • Normal heart beats begin at the SA node, which acts as the hearts "pacemaker."
  • The electrical impulse spreads across the right atrium and the left atrium.
  • The impulse travels through the AV node to the Bundle of HIS.
  • The Bundle of HIS divides into a left and a right bundle branch. The impulse spreads through these bundle branches into the purkinje fibers (purr-kin-gee) in the ventricles, the bottom chambers of the heart.
When the electrical impulses of the heart spread in a normal fashion from the top chambers down through the bottom chambers, this results in pumping of the blood out of the heart to the rest of the body.


Your heart's main functions are to receive oxygen-poor blood from your body and to pump oxygen-rich blood to nourish the body. To do this well, your heart needs to be strong with a regular heartbeat. Your heart needs working valves to control blood flow and blood vessels to transport blood to all parts of the body. Take good care of your heart so that it can take care of you. Talk with your doctor to learn more about taking care of your heart. Talk to your doctor or others on your health care team if you have further questions.