Electronic cigarettes, an increasingly popular option among smokers trying to quit, do not appear to pose a threat to the heart, according to results of a clinical study presented on Saturday.
Greek researchers said e-cigarettes - battery-powered metal tubes that transform liquid laced with nicotine into vapour - had no adverse effects on cardiac function in their small trial.
"Electronic cigarettes are not a healthy habit but they are a safer alternative to tobacco cigarettes," Dr Konstantinos Farsalinos from the Onassis Cardiac Surgery Center in Athens told the annual meeting of the European Society of Cardiology.
"Considering the extreme hazards associated with cigarette smoking, currently available data suggest that electronic cigarettes are far less harmful and substituting tobacco with electronic cigarettes may be beneficial to health."
Farsalinos and his team examined the heart function of 20 young smokers before and after smoking one tobacco cigarette against that of 22 e-cigarette users before and after using the device for seven minutes.
While the tobacco smokers suffered significant heart dysfunction, including raised blood pressure and heart rate, those using e-cigarettes had only a slight elevation in pressure.
The Greek clinical study was the first in the world to look at the cardiac effects of e-cigarettes. Another small study, also in Greece, reported earlier this year the devices had little impact on lung function.
Farsalinos acknowledged bigger studies were still needed to examine the possible long-term effects of e-cigarettes, while other doctors attending the medical meeting in Munich were cautious about giving them a clean bill of health just yet.
"Obviously, the e-cigarette has the advantage of not having the thousands of other chemicals, besides nicotine, that a real cigarette has," said Dr Russell Luepker of the University of Minnesota.
"I don't think it's conclusive but there's no doubt if you expose someone to fewer bioactive chemical compounds there is going to be less effect."
E-cigarettes were first made in China in 2003 but are now sold around the world and used by millions of people.