A lot of so-called heart attacks in younger people are actually sudden cardiac arrest, which is often caused by an actual heart attack (blocked artery) but can also occur due to anything that disrupts the normal electrical activity, often due to some defect in the electrical system which may go undiagnosed until it is too late (this is the first thing I always think of when I hear that somebody under 30 suddenly died), or even an extra heartbeat (which are very common in healthy people) that occurs at the right (or wrong) time.
Since the heart’s a pump, and when a pump fails fluid backs up on the intake side, it’s not unusual for the presenting complaint to be shortness of breath. People come in to the ER with pumonary edema caused by pump failure caused by the death of a chuck of muscle caused by the heart attack they had 3 days ago.
Diabetics are known to have an increased risk of silent MI.
An old friend of the family (fortunately, not blood related) had his first heart attack at age 18 and had heart trouble throughout his life. He lived to his 60’s though.