April 21 (HealthDay News) -- A compact heart assist device designed to fit women and smaller men has been approved by the U.S. Food and Drug Administration.

Heart assist devices are implanted mechanical devices that help weakened hearts pump blood while heart failure patients await a heart transplant. Previous models were too large to fit the upper abdomen of women and men of smaller stature, the FDA said.

The HeartMate II Left Ventricular Assist System is just 3 inches in length and weighs about 1 pound. A cable that powers the device passes through the patient's skin to an external controller, allowing the device to be powered either by battery or while connected to an electrical outlet.

In clinical testing on 126 people, 57 percent survived to undergo a heart transplant, which the FDA said is comparable to larger heart assist devices.

The manufacturer, Pleasanton, Calif.-based Thoratec Corp., will be required to conduct a post-approval study of the device's performance, the agency said.