Where is the first electrical wave in the heart initiated?

Sinoatrial Node

Explanation:

The sinoatrial node is like the natural pacemaker of the heart because it controls the heart beat or in other words, the cardiac rhythm. The sinoatrial node is found on the right atrium and it sends signals to both atria and then they contract. The signal is then carried to the atrioventricular node which spreads the signal to the ventricles and then the ventricles contract. The contractionof the ventricle is the pumping action of the heart.