This question is very important ...it is in forefront of the heart related diseases worldwide..

Why do heart muscles do not repair ,contrast to other muscles of the body which can repair after an injury or accident?

This happens because the heart muscles have specialized cells called as cardiomyocytes-----we will break the word,cardio-heart,myo-muscles,cytes -cells.
This cells do not regenerate after an injury ,if scientist are able to find some method by using stem cells or any other process to solve this complex mechanism it will be amazing discovery to solve the heart related problems.