It really depends on a whether you already have CAD or not. If you don't, then there are a lot of things you can do which will improve your likelihood of NOT getting the disease. Rather than medication, it's more to do with how you look after your body. If you put rubbish into your body and stress your body, it will respond in ways undesireable.
If someone already has CAD, then they will always be in the high risk zone for heart attack, or stroke with or without medication.
If you are talking about something preventative that can be taken now to limit the possiblity of a possible heart attack in your future or minimize the risks that could be a tough one. Heart attacks are generally caused by a blockage or narrowing of the arteries leading into the heart and is usually caused by either a plaque build up or clots. There is no way anyone but a doctor would know which one it is thru testing but there is preventative measures that you can take under the supervision of your doctor. One would be to keep your cholesterol levels down and maintain a healthy lifestyle as well as good eating habits and abstain from smoking and as far as that point goes no doubt it would be a medicine that the doc would prescribe to you if your cholest. levels are up in the way of a cholest. buster and if it were a clot issue the docs can either tell you to take an aspirin a day or some sort of blood thinner to minimize the risk of clots.....if you are talking about a med that you can take when you suspect you are having a heart attack that one is simple...you call 911 so medical professionals can do their job and save your life. You needed to be a little more specific with your question i think......