INDIANAPOLIS – A company under fire for not telling heart patients about a problem with its implanted defibrillators said Friday that 50,000 of the devices could be flawed and offered to replace more than half of them.

At least two patients with defibrillators made by Guidant Corp. have died, and the company said its devices had failed at least 45 times. Guidant said it was advising physicians about the safety of several models.

The Indianapolis-based company said, if requested, it would replace 28,900 of the implanted defibrillators that could develop a short circuit. More than 20,000 of those are used by Americans.

Another 21,000 devices – 18,000 used by U.S. patients – can be reprogrammed without being removed to fix a potential computer memory error, the company said.

The Food and Drug Administration advised patients to talk to their doctors and said it would not recommend whether individual patients with one of the recalled devices should have them removed and replaced. The company said anyone who recently received a defibrillator shock should consult his physician.

“This is a voluntary recall,” FDA spokeswoman Julie Zawisza said. “We’re in complete agreement that they need to do that.”

An implantable defibrillator, smaller than a pack of cigarettes, is intended to sense an irregular heart rhythm and shock the heart back into correct beating. Vice President Dick Cheney has one made by another company, Minneapolis-based Medtronic.

Candidates for defibrillators include those who have had a heart attack or who have had an episode of rapid heart beating or are at risk for that, experts said. The devices are implanted under the collarbone and one or more wires are threaded into the chambers of the heart.

Dr. Kenneth Ellenbogen, professor of medicine at the Virginia Commonwealth University School of Medicine in Richmond, Va., said the best thing for a patient with one of the recalled devices to do is talk to an electrophysiologist, a cardiologist who is a specialist in the field of devices and heart rhythm abnormalities.

Guidant came under fire this spring after The New York Times reported that it failed to alert physicians about a potential problem with the Ventak Prizm 2 DR model defibrillator.

Friday’s recall includes that model and the Contak Renewal and Renewal 2. Those models will be replaced at no charge because of the short-circuit problem.