Even through the heart is myogenic, it is still supplied by nerves from the sympathetic and parasympathetic nervous system. What are the sympathetic and parasympathetic nerves in the heart?
The sympathetic are the cardiac nerves and they go to the ventricle. These increase the force of contraction and help to dilate the coronary vessels during excersize. Can increase HR up to 230 beats/min.
The parasympathetic are the vagus nerves. They help to give the heart it vagus tone, which helps keep the heart at its normal HR. So it slows the heart down. If the vagus is cut the heart rate will increase to about 100 beats/minute.