Which layer of heart is affected in heart attack ?

The Inner One: Blood vessels run from the outside of the heart to the inside, so the area that gets hit first is what we call "endocardium" - it's the layer of heart muscle on the inside of the heart chambers. That said, that's only where the damage starts. Depending on the severity of the heart attack, it can involve the entire thickness of the heart wall.

Layers: There are some that only affect the inner layers and some that are full thickness or transmural.