Key points from article :
Daily e-cigarettes use double the risk of heart attack compared to non-smokers.
Smoking regular cigarettes daily nearly tripled their heart attack risk.
E-cigarettes deliver lower levels of carcinogens than regular cigarettes.
But still release small particles and toxins that damage blood vessels and encourage clotting.
Studied nearly 70,000 people who took part in two National Health Interview Surveys.
Published in American Journal of Preventive Medicine.