The Food and Drug Administration is warning doctors and patients about a commonly used antibiotic used to treat bacterial infections.
The drug is commonly sold under the name Zithromax or Z-Pak.
It's widely used to treat bronchitis, pneumonia and other infections.
FDA officials say doctors should consider prescribing other antibiotics to patients at risk with heart problems, or those with irregular heartbeats or low levels of potassium in their blood.
The warning was issued after the FDA reviewed two studies on the drug.
A Vanderbilt University study found an increased risk of death from heart disease in the first five days of using a Z-Pak when compared to other common antibiotics or no antibiotics.
Pfizer, which produces the drug, said the majority of patients using the antibiotic are not affected.