Probably the most avoidable risk factor today is cocaine abuse. Cocaine, and probably other similar stimulants, can cause heart attacks and arrhythmias. Stopping the use of cocaine reduces your risk of heart disease immediately. Other risk factors that can be controlled are smoking cigarettes, obesity, poor physical condition, and high blood pressure. Diabetics in good control may have less risk than those whose blood sugar isn't well controlled.
Stress reduction can be helpful as well.
As important as healthy habits and reduced risk factors are, in an emergency, seconds count. Know your local EMS system and how to access it. For more information, see the American Heart Association Web Page I recently got chest pain and went to the emergency department. My HMO refused to pay for the visit, and said that I should have called them first.