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On this page: Ventricles, Atria, and Valves | Blood Flow Thru the Heart | Circulation in the body | Coronary Arteries | Videos

The Ventricles, Atria, and Valves of the Heart

Illustration of the heart

The heart is a muscle that pumps oxygenated blood and nutrients to the body's cells. The heart muscle contracts and relaxes with each heartbeat.

There are four chambers in the heart: the top two chambers are called the right and left atria, and the bottom two chambers are the right and left ventricles.

There are four valves which maintain the free flow of blood in a forward direction through the heart chambers, then out through the arteries.  The valves open to allow blood to move in a forward direction, then they close tightly to prevent a backwards flow of blood. 

Arrow pointing to paragraph The opening & closing of these valves creates the heart sounds, Lub Dub. These sounds are best heard by the use of a stethoscope.

Illustration courtesy of NIAAA/Chung, M.K., and Rich, M.W. Introduction to the cardiovascular system. Alcohol Health and Research World 14(4):269–276, 1990.


Blood Flow Through the Heart

1) Oxygen-poor blood returns from the body,  flows into the heart through the right atrium.   During this time the tricuspid valve is closed, allowing the blood to fill the right atriumImage of heart 2) The muscle walls of the right atrium  contract and push the blood through the tricuspid valve and into the right ventricleImage of heart
3) Once the right ventricle has filled with blood,  the right ventricle contracts and pushes the blood through the pulmonic valve, into the pulmonary artery.  This artery divides and transports the blood throughout the lungs.  In the lungs, the blood gives up carbon dioxide in exchange for oxygen.Image of heart 4) The oxygen-rich blood is then returned from the lungs to the left side of the heart, into the left atrium.  During this time, the mitral valve is closed, allowing the blood to fully fill the left atrium.Image of heart
5) Contraction of the heart muscle of the left atrium pushes the blood out of the left atrium, past the mitral valve, and into the left ventricle. Image of heart 6) Once the left ventricle is full of blood, the muscle walls contract pushing the blood past the aortic valve, into the aorta, and out into the body.Image of heart
Both the left side and the right side of the heart contract at the same time, in a balanced symmetry.  The coordination of these events is determined by the electrical activity which originates in the right atrium and moves throughout the heart.  The electrical impulses that cause the heart muscle to contract are measured by an EKG.  The opening and closing of the valves generate the heart sounds.  These heart sounds are best heard with the use of a stethoscope.  Damaged valves can cause turbulent blood flow  and are called heart murmurs.

The heart pumps blood through the body's arteries
Blood Flow Through the Body: The heart muscle pumps the circulating blood
through the heart, lungs, and throughout the body. 

Arteries: The oxygen-rich blood is transported thoughout the arteries of the body by the pumping action of the heart.

Veins: Once the oxygen has been released into all the tissues of the body, the oxygen-poor blood is then transported by the veins back to the right side of the heart.

Heart and Lungs: Blood comes into the right atrium from the body, moves into the right ventricle and is pumped into the pulmonary arteries in the lungs. After waste gas (carbon dioxide) is removed and oxygen is picked up from the lungs, the blood travels back to the heart through the pulmonary veins into the left atrium, and finally to the left ventricle.

Aorta and Body: The left ventricle contracts and pushes the blood through the aorta and out to the body's tissues and general circulation.

Illustration courtesy of the National Institute of Diabetic and Digestive and Kidney Diseases

Blood Flow Around the Heart in the Coronary Arteries:

Although the inside chambers of the heart are full of blood, the heart muscle itself is fed from a network of blood vessels on the surface of the heart. These blood vessels are the coronary arteries.

The oxygenated blood that leaves the heart is pumped from the left ventricle into the aorta which immediately sends of branches, referred to as coronary arteries. These very important arteries surround the hearts surface and and deliver oxygenated blood to the vital heart muscle.

The branches of coronary arteries are first divided into two major coronary arteries, the Left Main and the Right Coronary Artery. The Left Main then divides into the Left Anterior Descending (LAD) and the Circumflex.

Anterior Coronary Arteries
Anterior Corornary Arteries supplying the muscles in the front of the heart

Posterior Coronary Arteries
Posterior Coronary Arteries supplying the blood flow to the muscles in the back of the heart

The coronary arteries are often the source of signficant disease. In fact, coronary heart disease is America's No. 1 killer.

Read more about disease of the coronary arteries: coronary heart disease (also known as coronary artery disease).

Calculate your Cardiac Risk

Video Tutorials

Animated illustrations of the heart from the American Heart Association. View excellent captioned illustrations and animations of conditions, treatments and procedures related to heart disease.

Animated Heart, Narrated Tour from Largo Medical
This is an excellent well-illustrated animated video of blood flowing through the atria & ventricles.

Diseases and Anatomy of the Heart from Medline Plus, A Service of the National Library of Medicine and National Institute of Health. This site has an extensive list of videos related to heart conditions, cardiac surgical procedures, cardiac diagnostic procedures and cardiac wellness topics that are excellent patient education resources. 

Images and Case Studies

--Written by N Thompson, ARNP in collaboration with M Thompson, MD, Internal Medicine, Updated January 2010

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