From the American Heart Association:
Heart attack and stroke are life-and-death emergencies — every second counts. If you see or have any of the listed symptoms, immediately call 9-1-1 or your emergency response number. Not all these signs occur in every heart attack or stroke. Sometimes they go away and return. If some occur, get help fast! Today heart attack and stroke victims can benefit from new medications and treatments unavailable to patients in years past. For example, clot-busting drugs can stop some heart attacks and strokes in progress, reducing disability and saving lives. But to be effective, these drugs must be given relatively quickly after heart attack or stroke symptoms first appear. So again, don’t delay — get help right away!