If you use an electronic cigarette, here are two new reasons to consider quitting: Daily e-cigarette use can double the risk of a heart attack. Also, using e-cigarettes and regular cigarettes together appears to be more dangerous than using either product by itself, researchers have found.

In the first study examining the link between heart attacks and e-cigarettes, researchers at the University of California – San Francisco analyzed the smoking habits of more than 9,000 current and former e-cigarette users. About two-thirds of e-cigarette users were also smoking cigarettes.

E-cigarettes deliver a vapor that contains lower levels of cancer-causing substances than regular cigarettes but they also emit other particles and toxins linked to cardiovascular and lung disease risks. Using both products daily made the odds of having a heart attack almost five times greater than for those who had never used either product, they found.

But the news isn’t all gloomy: Unlike those who use regular cigarettes, there is no ongoing, heightened risk of heart attacks among e-cigarette users who quit. That may be because the health risks of e-cigarettes go away more rapidly when someone quits or because many people quit e-cigarettes before any lasting damage is done.

For all smokers, there’s immediate value in quitting the habit. The risk of heart attack starts to drop immediately upon quitting — and, researchers noted, that’s true for both electronic and conventional cigarettes.

So while vaping may be a way to wean yourself off traditional cigarettes, it’s not without hazards of its own. The best advice is not to pick up the unhealthy habit to begin with.