mechanism of negative chronotropic effect ↓Ca→ Lautomatic depolarization mechanism of negative dromotropic effect T ERP of Atrioventricular node purkinje fibers i conduction mechanism of negative inotropic effect atrium:↑K+efux>↑ repolarization action potential duration l, ERPV, Ca2+v ventricles: presynaptic membrane M-R NA releasemechanism of negative chronotropic effect ↓Ca2+ →↓automatic depolarization mechanism of negative dromotropic effect ↑ ERP of Atrioventricular node & Purkinje fibers →↓conduction mechanism of negative inotropic effect atrium: ↑ K+ efflux→ ↑ repolarization → action potential duration ↓ , ERP↓，Ca2+ ventricles: presynaptic membrane M-R →NA release↓