The heart is a centralized organ, in the chest, in vertebrates, which is the primary mechanism of circulating the blood throughout the body. It is composed of a special type of muscle tissue, which is called the cardiac muscle and this muscle is only found in the heart. Heart disease causes more deaths than any other form of disease and it is the number one cause of death amongst Americans.http://my.clevelandclinic.org/heart/heartworks/heartfacts.aspx

Smoking cigarettes can be a cause of heart disease and heart failure. Enlarged hearts can result from exercise or disease. A wide range of ailments can affect the heart, including Kawasaki Disease and Cardiomyopathy. Mammals and birds have four chambers, amphibian hearts have three, and fish hearts have only two.http://my.clevelandclinic.org/heart/heartworks/heartfacts.aspx

The human heart is separated into four chambers, two of which whose purpose is to operate by pumpin the deoxygenated blood, throughout your body, back around and into the lungs (where they absorb oxygen), and the other two pumps are there to pump the oxygenated blood to all of the other tissues of the body.

Deoxygenated blood enters the right atrium, moves to the right ventricle, and then is moved to the lungs. From the lungs, it passes to the left atrium, then moves to the left ventricle, then is pumped to the rest of the body. Once the body has absorbed the oxygen, the blood enters the heart and begins the cycle anew.

• WebMD: Heart Health Center