Dr. Wayne Ray, professor of Health Policy at Vanderbilt University, said, "for every million courses of clarithromycin there were 37 additional cardiac deaths."
Clarithromycin is used to treat common bacterial infections. It belongs to a group of antibiotics that can interfere with electrical activity of the heart muscle.
"Patients with heart problems are the ones who should be most aware of this adverse effect and for these patients it will become more important in deciding which antibiotic to use," Ray said.
Researchers stress the risk is small and say doctors should not change the way they prescribe the antibiotic until their findings are confirmed.
The FDA warned patients last year about another common antibiotic azithromycin, saying it could contribute to a deadly irregular heartbeat, especially in patients with heart problems.
Ray authored the study the FDA reviewed and says all antibiotics have risks, so patients should talk to their doctors.