My 2 son yr old banged his sternum yesterday. He's fine, but is there a danger of cardiac problems?

He's not in any pain. I think, from looking at his chest, that it was perhaps more of a graze than a direct blow - he just has slight redness and minor abrasions. I have heard of people having heart attacks after a blow to the sternum. I wondered if I should take him to the doctors. My wife thinks that since he's showing no sign of discomfort or unhappiness that there's no need.