My dad had a massive heart attack at 42. my mom had 1 at 50. what might my chances be of having one?

Heart disease: You are at increased risk due to hereditary factors that you may have. You should see your doctor about a preventative program. Examination and blood tests etc. Can determine if you have increased risk factors. A program of a healthy life style, nutritious diet, proper exercise and controling any risk factors can be developed for you. Prevention is the key to maintain good health.

Depends on you: You have a strong family history ('bad genes'), but your fate is not sealed. If you control your risk factors (no smoking, maintain a healthy body weight with a body mass index 21-25 kg/m2, exercise 45-60 min/day x 5-7 days a week, maintain a low LDL - bad - cholesterol, make sure you don't get high blood pressure or diabetes), than you may never get a heart attack despite your family history.