How does a heart attack potentially cause Heart Failure?

If you have had a heart attack, then it may be that there's been damage to part of the heart muscle. If that part of the heart muscle is damaged, then it can't contribute to the overall pumping of the heart and pumping and help in pumping blood around the rest of the body. So if you think of the heart muscle like this, if there's an area of scar because of a heart attack then this part won't be able to contribute to how well the heart is pumping to get blood around the rest of the body. Hence a heart attack can cause and contribute to heart failure because the overall fraction of blood that the heart pumps out will be less. Of course it depends on the size of the heart attack and some heart attacks don't necessarily leave too much damage in the heart if the heart attack is treated quickly enough.