Mouth to mouth

Such an act dramatically increases the chances of the victim dying because it stops you from pushing down on the chest, which is the only lifesaving action that might actually work in such an extreme situation.

Chest compression has proved to be the most effective technique in various studies—yet, doctors continue to recommend mouth-to-mouth as part of emergency first-aid care for heart-attack patients.

Why is that? It may be because physicians treat all sudden and life-threatening attacks the same—but, of course, they’re all different, despite having superficial similarities. 

Someone who has nearly drowned or overdosed on drugs may look like a heart-attack victim, but there’s one big difference. In these cases, the patient has usually stopped breathing, so mouth-to-mouth combined with chest compression is absolutely the right thing to do.

But most heart-attack victims are still breathing very lightly, or gasping, so mouth-to-mouth is not only un-necessary, it may also increase the chances of death (Lancet, 2007; 369: 882–4).