The heart is one of the strongest muscles in the body. Even when removed from the body it continues to beat for quite a while. It has back-up systems: even if the sinus node fails secondary circuits take over.
Of course we should do everything we can to keep our heart healthy. If we have a major problem we should work closely with our GP and cardiologist. Other than that we should have confidence and reassurance in the fact that the heart is not a delicate instrument, it's as tough as old boots.