How Your Heart Functions
The heart is about the size of your fist and weighs between 200 and 425 grams. There are four heart chambers which include the right and left atria (top chambers) and the right and left ventricle (bottom chambers). The valves separating the top and bottom chambers are the tricuspid valve on the right side of the heart and the mitral valve on the left side of the heart. The 2 other valves are the pulmonic valve and the aortic valve. The pulmonic valve allows blood to flow from the right ventricle to the lungs to be oxygenated. When the oxygenated blood returns from the lungs it enters the left side of the heart and is ejected through the aortic valve into the aorta and to the rest of the body.
The heart is the most important muscle in the body. It continuously pumps blood throughout the body and carries essential nutrients and oxygen to your organs, tissues, and cells. The heart receives its nutrients and oxygen through the coronary arteries.
Healthy coronary arteries have inner linings which allow the blood to flow smoothly. Damage to the lining of the coronary arteries makes them rough, which allows cholesterol and fatty substances to stick and collect in them. This may also cause plaque to form which contributes to narrowing of these arteries and the development of atherosclerosis and coronary artery disease. These changes to the arteries then may play a role in the development of other heart conditions such as angina, myocardial infarction (heart attack), and rhythm disturbances to name a few.
The heartbeat starts in the Sinoatrial Node (SA node) located in the top chamber of the heart (atria) releasing an electrical signal that spreads to the right and left atria. The signal pauses at the Atrioventricular Node (AV node) in between the top and bottom chambers (ventricles) and proceeds to the right and left ventricles. The electrical signals cause each chamber to contract pushing the blood to the lungs and body.
As the blood moves from the top chambers to the bottom chambers it passes through the heart valves. These valves prevent from the blood from flowing in the wrong direction. Each heart valve is made up of leaflets or cusps that open and close about 100,000 times each day. The four heart valves are the tricuspid, pulmonic, mitral, and aortic valves. A heart valve is said to be "malfunctioning" when it fails to fully open or close.
There are many reasons why people may have abnormalities with the heart valves. This abnormality could have been present at birth (congenital), or been a result of other diseases which attack the valves of the heart such as rheumatic fever and endocarditis.
When the valves are affected by disease there may be stenosis (abnormal narrowing) or prolapse (bulges backward into the upper chambers). The heart then needs to work harder to push the blood through the heart and to the rest of the body. This additional workload on the heart can cause the heart muscle to increase in size (enlargement) and lead to other complications.
Texas Heart Institute- Anatomy of the Heart
Stanford Health Library-Cardiovascular