How long does it take heart muscles to function again after a heart attack?

No, dead muscle is dead muscle - however the genius of the human body is that it can adapt. If there is enough of the heart sill alive it will increase its effort to compensate for what died. Many people live long lives after heart attacks. It is best to catch an attack before the muscle dies and have surgery to rework blood paths to the starved muscle. Bypass and shunts have worked restoring blood flow to struggling hearts restoring health and longevity. But a dead muscle is a dead muscle so treatment before a major attack is critical.