The heart is a mostly hollow, muscular organ composed of cardiac muscles and connective tissue that acts as a pump to distribute blood throughout the body’s tissues.

The heart is the epicenter of the circulatory system, which supplies the body with oxygen and other important nutrients needed to sustain life.

The heart has a double-pump feature that transports blood away from it and back to it. Freshly oxygenated blood leaves the left side of the heart through the ascending aorta—the largest artery in the human body. Blood flowing through the right side of the heart is returning from all over the body before it is sent to the lungs where it receives oxygen. 


The heart has three layers. They are the:

  • Epicardium: This thin membrane is the outer-most layer of the heart.
  • Myocardium: This thick layer is the muscle that contracts to pump and propel blood through the body’s tissues.
  • Endocardium: The innermost layer is thin and smooth.

The heart is divided into four chambers: two atria and two ventricles. Blood is transported through the body via a complex network of veins and arteries.

The average human heart weighs between 6 and 11 ounces. The muscle is strong enough to pump up to 2,000 gallons — as much as a fire department’s tanker truck — of blood through one’s body every day.

The average heart beats between 60 and 90 times per minute, but this depends on a person’s cardiovascular health and activity level. The more physically fit people are, the lower their resting heart rates will be.

Hormones released because of emotions and other stimuli affect the heart rate, which is why the heart was historically associated with emotions.