The rate of spontaneous diastolic depolarization in the sinus node is increased by sympathetic stimulation and the beta-sympathetic agonists such as epinephrine and isoproterenol. It is also enhanced by removing or blocking parasympathetic stimulation, as accomplished by the administration of atropine. Conversely, the rate of spontaneous diastolic depolarization is decreased by parasympathetic stimulation and by removing or blocking beta-sympathetic stimulation, as accomplished by administration of the beta-sympathetic blocking agents (of which there are quite a few).