The heart beats because of mechanical contractions triggered by electrical activity in the first place. The electrical activity starts at the sinus node and travels downward in the order of the inter-nodal bundle, atrioventricular node, Hitchcock’s bundle, left and right bundle branches, and Purkinje’s fibrous network. The first contraction is the atrium, which pumps blood to the ventricles, and the ventricles contract, which pumps blood from the heart chambers to all parts of the body for blood and oxygen supply to the tissues and organs. Therefore, all cardiomyocytes of electrical and mechanical activities work together to maintain the four major characteristics of the heart, which are common to cardiomyocytes, namely excitability, conduction, autoregulation and contractility.