well heartfluttersflyawayplz answered the question correctly, whether test or not. Some area of heart muscle was without oxygen for too long and died. Heart muscle once dead cannot regenerate.
I don't know if this is a real question or you're looking for an answer on a test.
Why does this sound so much like a test question?
only a dr can tell you this , but i would think its from the heart not getting enought blood to it and damaging that part of the muscle. some time in certain areas the heart will not repair its self ,so what ever damage is done is done. hope you find your answer.