Myocardial depression may occur with excessive doses of all local anesthetic agents, but certain drugs, such as bupivacaine, may also produce ventricular arrhythmias associated with cardiovascular collapse. The current study was designed to assess the electrophysiologic effects of both bupivacaine and lidocaine on ventricular muscle and Purkinje fibers.Right ventricular septal walls, including the right bundle branch and papillary muscle, were dissected out from fresh cardiac specimens of rabbits and suspended in a nutrient bath. Recording glass microelectrodes were inserted into Purkinje fiber cells and ventricular muscle cells for eventual display of action potentials. The preparation was paced at an amplitude twice threshold. Parameters determined included maximum diastolic potential (MDP), action potential amplitude (AP), maximum rate of depolarization &OV0312;max) and action potential duration (APD). Other data derived included effective refractory period (ERP), membrane responsiveness, and Purkinje fiber-ventricular muscle conduction (PF-VM).