In this case, the device was implanted into a pig by way of the internal jugular vein.
A heart working at the rate of 80 beats per minute generated 4.3 microjoules of energy per cardiac cycle, about 17 percent of the electricity needed to run a pacemaker.
When the heart beat faster, more energy was produced, and when the heart beat slower or blood pressure was reduced, the corresponding energy produced declined.
The device appeared to cause no harm to the heart.
"The study is very preliminary," said American Heart Association spokesman Dr. Gordon Tomaselli, a professor of medicine in the division of cardiology and molecular medicine at the Johns Hopkins University School of Medicine in Baltimore. "People aren't going to change manufacturing based on this data."
But researchers are currently changing the materials of the microgenerator in the hopes of producing all the energy an implanted pacemaker or defibrillator needs.
The American Heart Association has more on pacemakers.
SOURCES: Ann F. Bolger, M.D., American Heart Association spokeswoman and William Watt Kerr professor of clinical medicine, University of California, San Francisco; Gordon Tomaselli, M.D., co-director, Donald W. Reynolds Cardiovascular Clinical Research Center, and professor, medicine, division of cardiology and molecular medicine, Johns Hopkins University School of Medicine, Baltimore; Nov. 10, 2008, presentation, American Heart Association annual scientific sessions, New Orleans
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