1.NounAn acute myocardial infarction, sometimes fatal, caused by the sudden occurrence of coronary thrombosis, which obstructs the blood supply to the heart and leads to necrosis of heart muscle tissue.
2.NounA major fright.
"She'll have a heart attack when she sees that!"
3.NounDeath or failure.
"My computer had a heart attack when I tried to get it to run that program."