A person can still have a heart attack while wearing a pacemaker or defibrillator. A heart attack, or myocardial infarction (MI), happens when a blood vessel blockage cuts off the blood supply to an area of the heart muscle. It can result in the death of some cells in that area. Pacemakers and defibrillators help correct heart rhythm abnormalities, not blood vessel blockages. So a person can still experience an MI with an implanted cardiac device.