re: Heart attack in your 30s?

Please define "relatively healthy" and "overweight" as you want them to be used in this answer. If you use "no significant PMH, does not take any medication, does not use drugs, does not smoke" and "BMI <25," the answer is "extremely rare." The main cause coming to mind here is an ASD leading to a clot from the legs (your lungs usually act like a filter for really little ones, and they don't really bother the lungs, the ones that I am talking about) going through the ASD and into the left side of the heart, then into coronary circulation. I don't know numbers, but I think strokes are more common in this group than heart attacks. Both pretty rare, but probably the most common cause in someone using my definition for your words.