Updated December 29, 2014.

The heart is a large, muscular sac located approximately in the middle of the chest, above the level of the breasts.

Structure:

The heart is hollow, and the inside of the heart is divided into four separate chambers by thin, muscular walls. If you picture the heart as a simple square, there are two upper chambers and two lower chambers, all of which fill with blood at different times during the cardiac cycle.

The top chambers of the heart are collectively called atria and the bottom chambers are called ventricles. The four chambers of the heart are the

• Right Atrium
• Right Ventricle
• Left Atrium
• Left Ventricle

Function:

The heart is the pump which drives circulation by contracting and squeezing blood out into the body.

Special Properties:

The heart is a muscle, and shares many properties of the other muscles in the body. Just like any other muscle, the harder the heart works, the bigger and thicker it will get. This can lead to problems like a heart attack

Continue Reading: Part Two: Arteries