The function of the natural heart can be divided into interdependent halves. Oxygen-poor blood returns via the veins to the right side of the heart, where it is pumped to the lungs. Oxygen-rich blood from the lungs returns to the left side of the heart where it is pumped out into the body. The two halves of the heart can fail separately or together. Some devices can be implanted in either the right or left side or both sides simultaneously.
Some devices work well only on the left side.
Most of the work of the heart is accomplished by the left side so the majority of devices are designed to assist left heart function. However, right heart failure can be deadly and heart surgeons need to have a device strategy ready to deal with both types of failure. Currently the TCI HeartMate, and the Novacor and Thoratec pumps are the only assist devices approved by the F.D.A. Approved use of these device is restricted to patients awaiting heart transplant. The electric powered version of the HeartMate pump might be able to work as a long-term left heart assist device. Experience in European and U.S. trials has suggested that some patients can return to home, school and work with the device in place.