Puffing just one e-cigarette with nicotine can cause damage to the heart of nonsmokers, a new study suggests.

The study included 33 healthy nonsmokers. On different days, participants used an e-cigarette with nicotine, an e-cigarette without nicotine or an empty device. Researchers measured adrenaline levels in the heart. They found participants had a pattern of abnormal heart rate variability, indicating increased adrenaline levels, after they used the e-cigarette with nicotine. They determined the increased levels were due to the inhaled nicotine and not the non-nicotine components of the e-cigarette aerosol, Newsweek reports.

The findings appear in the Journal of the American Heart Association.

“These findings challenge the concept that inhaled nicotine is benign, or safe,” senior study author Dr. Holly Middlekauff of the David Geffen School of Medicine at UCLA said in a news release.