First off, I just want to say in no way is full flush retarded. I really highly doubt he's shoving less than A4 here if even that. I guarantee he'd shove AJ because I feel like not doing that would be dumb. At the same time, okay, he could be bluffing you off A4/A2. He could also have missed a gutshot or something like that and is trying to bluff you off a miss heart draw. Both of these are pretty doubtful. But given your getting like 2.5 to 1 and I'd say his most likely hand is AJ I'd call.