Atrial natriuretic peptide (ANP) has varied effects on cardiac electrophysiologic parameters including heart rate, intraatrial conduction time, and refractory period. ANP's vagoexcitatory and sympathoinhibitory actions as well as its direct actions on cardiac ion currents may be responsible for some of these effects. This review discusses the role of ANP in cardiac electrophysiology, its interactions with the autonomic nervous system and baroreceptor reflex, and its effects on cardiac ion currents.