Myocyte coordinate contraction throughout the remaining heart muscle via the electrical conduction system of the heart. Sinoatrial node activity is modulated, in turn, by nerve fibres of both the sympathetic and parasympathetic nervous systems. These systems act to increase and decrease, respectively, the rate of production of electrical impulses by the sinoatrial node. There are numerous methods employed for fiber-typing, and confusion between the methods is common among non-experts. Two commonly confused methods are histochemical staining for myosin ATPase activity and immunohistochemical staining for Myosin heavy chain (MHC) type. Myosin ATPase activity is commonly—and correctly—referred to as simply "fiber type", and
Heart development before the fusion of the endocardial tubes. The heartbeat begins in the region of the pacemaker which has a spontaneous depolarization time faster than the rest of myocardium. The primitive ventricle acts as initial pacemaker. But this pacemaker activity is actually made by a group of cells that derive from the sinoatrial right venous sinus. These cells form an ovoid sinoatrial node (SAN), on the left venous valve. After the development of the SAN, the superior endocardial cushions begin to form a pacemaker as known as the atrioventricular node. With the development of the SAN, a band of specialized conducting