How the Heart Works

The heart is an important pump. From the moment of development through the moment of death, the heart pumps. The heart muscle, also called cardiac muscle, contracts and relaxes an average of 70 to 80 times per minute. As the cardiac muscle contracts, it pushes blood through the chambers of the heart to the blood vessels. These blood vessels lead to all organs throughout the body. Nerves connected to the heart regulate the speed or rate at which the muscle contracts. For example, when you run, your heart pumps more quickly. When you are asleep, your heart pumps more slowly.

Taking into consideration how much work it has to do, the heart is surprisingly small. The average adult heart is about the size of a clenched fist and weighs approximately 11 ounces (310 grams). The heart is located in the middle of the chest behind the breastbone and between the lungs. It rests in a lubricated chamber called the pericardial cavity, which is surrounded by the ribcage. A tough layer of muscle called the diaphragm lies below. As a result, the heart is well protected.