Heart size varies with body size. The average adult’s heart is about 5.5 inches (14 centimeters) long and 3.5 inches (9 centimeters) wide, or approximately the size of one’s fist. The heart is located just above the diaphragm, between the right and left lungs. One-third of the heart is located on the right size of the chest, while two-thirds is located on the left side of the chest.