I have heard that some people die of a heart attack caused by extreme happiness. Is it possible?
Increased adrenaline, as previously discussed, may contribute to rupture of cholesterol plaques.
I can only assume that any stress to a heart on the brink of disaster can be a trigger that send it over the edge. Getting some piece of extremely good news like winning the lotto is bound to cause an elevation in blood pressure and heart rate that could trigger this.
However, I'm not sure if you are asking about a quick onset of extreme happiness like in the lottery example or if you just meant to ask if being an extremely happy person in general could cause you to be at a higher risk for a heart attack?
Dropping dead of a heart attack upon receiving some news of outrageously good fortune seems to be commonly assumed to be something that can and does happen but in searching for heart attack and lottery I was unable to find any documented stories of something like that happening, although there are plenty of documented stories of people dying from heart attacks weeks or months after winning a lotto.
This could be because of a newly active lifestyle or an increase in excessive indulgences with one's new found wealth.
In any event, given that any trigger that causes a substantial increase in heart rate or blood pressure is potentially a trigger for an unhealthy heart to go in to cardiac arrest, I think it's safe to assume that the answer to your question is yes, potentially, although there does not seem to be very many documented cases of this, or any published studies of the phenomena that I was able to find.