When a man arrived at the emergency room, it looked to doctors like he was having a heart attack. But that was a false alarm: The man had actually swallowed a battery that messed with his electrocardiogram (EKG), a measure of the heart’s electrical activity, according to a new report of the case. 

Once doctors removed the battery, the EKG returned to normal, according to the report, published Monday (Nov. 23) in the journal Annals of Internal Medicine.

“If someone swallows a single battery or multiple batteries, the electrocardiogram can mimic changes consistent with an acute [myocardial infarction, or heart attack],” said Dr. Guy L. Mintz, director of cardiovascular health and lipidology at Northwell Health’s Sandra Atlas Bass Heart Hospital in Manhasset, New York, who was not on the case. 

The 26-year-old man was a prison inmate who arrived at the emergency department of Santa Maria Nuova Hospital in Florence, Italy complaining of stomach pain two hours after intentionally swallowing a AA battery. There, having spotted the battery on an X-ray, doctors did an EKG, in which electrodes placed on the chest record the electrical activity of the heart and graph it as a squiggly line on a gridded background.