The heart is responsible for pumping blood through the blood vessels by repeated, rhythmic contractions. The heart is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart, beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime spanning 66 years.
The heart consists of four cavities called chambers, which consists of two atria and two ventricles. The right and left atria are situated on top, while the right and left ventricles are situated on the bottom. A wall, called the septum, separates the right and left sides of the heart. 
- the right atrium receives oxygen-depleted blood from the body
- the right ventricle receives oxygen-depleted blood from the right atrium and pumps it to the lungs
- the left atrium receives oxygen-rich blood from the lungs and pumps it into the left ventricle
- the left ventricle receives oxygen-rich blood from the left atrium and pumps it to the entire body
Physicians and nurses use stethoscopes to listen for heart sounds and murmurs . Numerous heart abnormalities, such as valvular problems can be detected. Usually such observations are confirmed by further diagnostic tests.