The majority of the human heart is located to the left of the center of the chest and behind the sternum. The remaining third of the human heart is on the right side of the mid-line of the chest.
The heart is a muscle that sits between the lungs and the breastbone. It is cone-shaped and hollow. There are three layers to the heart. They are the myocardium, endocardium and pericardium.
The endocardium is the lining of the heart. The middle layer of the heart is the myocardium. The pericardium is the fluid-filled sac that surrounds the other two layers.