There are two principal Types of Cardiac Action Potentials Fast-response action potentials: occurin atrial and ventricular myocardiac fibers and specialized conducting fibers(purkinje fibers) that exist mainly in the endocardiac surfaces of the ventricles Slow-response action potentials: occur in the sinoatrial (SA)node(sA), which is the natural pacemaker region of the heart and the atrioventricular(Av) node, which is the specialized tissue that conducts the cardiac impulse from he atria to the ventricles• Fast-response action potentials: occur in atrial and ventricular myocardiac fibers and specialized conducting fibers (Purkinje fibers) that exist mainly in the endocardiac surfaces of the ventricles. • Slow-response action potentials: occur in the sinoatrial (SA) node (SA), which is the natural pacemaker region of the heart; and the atrioventricular (AV) node, which is the specialized tissue that conducts the cardiac impulse from the atria to the ventricles. There Are Two Principal Types of Cardiac Action Potentials