This response is caused by stimulation of the right vagus nerve. After transmission excitation through parasympathetic ganglia ACh is released in the SA node of the heart. Slowing or stoppage of the heart ensues. The response is mediated by muscarinic receptors that activate potassium channels in the supraventricular cells of the heart. In the SA node, activation of potassium efflux causes hyperpolarization and/or decreases the rate of diastolic depolarization. Thus, heart rate is slowed.