Make a fist. You’ve just estimated the size of your heart. Yet this small organ — weighing less than a pound — can circulate a gallon of blood throughout your body, all day every day. It’s the engine that runs the circulatory system, one of your body’s ten systems.
The heart is essentially a muscular pump. It circulates the blood through the lungs, where oxygen is obtained, and on through blood vessels called arteries. This is how other organs and tissues receive oxygen and nutrients, and where carbon dioxide is removed from the blood.
The heart is in the center of the chest, between the lungs. The bottom of the heart, called its apex, points slightly toward the body’s left side. This tilt means about two-thirds of a heart’s mass is found on its left side. The left lung is slightly smaller than the right lung, and it has a notch in it where the heart sits.
All the blood delivered to the tissues from the heart goes through the aorta. The aorta is the body’s largest artery. It is located at the top, along with pulmonary arteries going to the lungs and veins.
The heart beats, or contracts and relaxes, an average of 72 times per minute. The heart has four chambers and four valves that allow passages of blood between the chambers and in and out of the heart. Valves open in only one direction to prevent blood from going the wrong way.
A healthy heart is critical to life. Thirty percent of all deaths in the world are caused by heart disease. Risks for heart disease increase for those who smoke; are obese; do little exercise; or have high blood pressure, diabetes, or high cholesterol. These risk factors build up fatty material inside the arteries. This buildup narrows the arteries, reducing blood flow.
What happens as a heart fails and becomes unable to perform its duties? In extreme cases, it is removed and replaced with another heart. This is known as a heart transplant. The first transplant was in 1967, by Dr. Christiaan Barnard, in South Africa.
Today, approximately 3,500 heart transplants are performed every year, more than 2,000 of them in the United States. Unfortunately, there are about 800,000 people with advanced heart failure. There are not enough available hearts from recently deceased people to allow transplants for everyone who needs one.
Over the years, many alternatives to heart transplants have been proposed, developed, and rejected. External pumps can keep patients alive while they wait for a human heart for transplant. The famous physician Michael DeBakey, based in Houston, Texas, was a heart surgeon who pioneered many new procedures and alternatives.
In 1982, the first successful implant of an artificial heart, the Jarvik-7, was performed. The artificial heart was implanted in a dentist, Dr. Barney Clark, who lived for 112 more days. He was connected to a 400-pound air compressor the entire time. The Jarvik-7 had been designed by a team including medical engineer Robert Jarvik.
Artificial hearts are not yet a long-term way of extending life, but development continues. In the meantime, they and other methods serve to help patients wait for a transplant.