Being idol is the worst thing you could do to your heart.  As a Paramedic I have taken way to many people to the E.R. with chest pains at an early age, when it could have been prevented.  Genetics does play a big role in whether or not you will have a heart attack later in life, but fortunately there are many things you can do to prevent a heart attack.  First and foremost, get up off the couch, turn the T.V. off and start moving.  Cardiovascular exercise is vital to keeping your heart healthy.  American Heart  recommends you do an exercise that elevates your heart at least 20 - 30 min three to five days a week.
Next kick out the bad habits.  Smoking is a big contributor to poor cardiac health.  It also makes exercise more difficult.  What are you eating?  Diets high in saturated fat will only clog the arteries that supply the heart and rob it of oxygen.  Stick to a diet that is high in omega-3 fatty acids like fish.  Reduce the amount of red meat in your diet and eat more lean meat like chicken breast or turkey.  Whole grains will help lower your cholesterol, like oatmeal, wheat, brown rice, nuts.  If your not getting enough green vegetables in your diet then your not getting the vitamins, minerals, and antioxidants you need.  Supplements are a great way to make sure your body is getting what it needs to keep your heart healthy.