We have studied the individual and combined effects of elevated external potassium concentration (8 mM [K+], metabolic acidosis (pH = 6.8), and hypoxia at different stimulation rates (BCL = 1,000 or 400 milliseconds) on Purkinje (P) and ventricular (V) conduction velocities and on Purkinje-ventricu-lar junctional conduction delay (PVJ delay) in in vitro preparations from canine ventricles. Elevated [K+] had opposite effects on P and V velocities, increasing V velocity by 8% while reducing P velocity by 7%. Acidosis reduced P velocity by 9% while reducing V velocity by only 4%. Hypoxia and rapid stimulation rates had no significant effect on either P or V velocities. All test solutions (except hypoxia alone) significantly increased the PVJ delay. The magnitude of the increase in PVJ delay was much greater than the effects on either P or V velocity. In addition, hypoxia and rapid stimulation augmented the increase in PVJ delay in the presence of elevated [K+] and/or acidosis. The special features of conduction at the PV junctional sites may produce altered pathways of excitation of the ventricles during myocardial ischemia.