While exercise is generally great for the heart and is regarded as the single most important thing a person can do to prevent heart disease, this is not true in every case. In this video, nutrition and fitness expert Janet Bond Brill, PhD, RDN, FAND, LDN, explains that—regardless of lifestyle interventions such as exercise and diet—genetics also play an important role when it comes to heart disease. If either of your parents suffered cardiovascular complications before age 50, you have a genetic predisposition to heart disease. In this case, exercise can be a stressor and actually cause a heart attack, so if you do this genetic link, you should see your doctor and seek preventive therapy. Diet, exercise and preventive medical care all go hand in hand in preventing heart disease, the number-one killer of American men and women.