Pulmonary vein (PV) cardiomyocytes play an important role in atrial fibrillation; however, little is known about their specific cellular electrophysiological properties. We applied standard-microelectrode recording and whole-cell patch-clamp to evaluate action potentials and ionic currents in canine PVs and left atrial (LA) free wall. Resting membrane potential (RMP) averaged -66 ±1 mV in PVs and -74±1 mV in LA (P<0.0001) and action potential amplitude averaged 76±2 mV in PVs vs. 95± 2 mV in LA (P<0.0001). PVs had smaller maximum phase 0 upstroke velocity (V_max: 98±9 vs. 259± 16 V s^-1, P<0.0001) and action-potential duration (APD): e.g. at 2 Hz, APD to 90% repolarization in PVs was 84% of LA (P<0.05). Na⁺-current density under voltage-clamp conditions was similar in PV and LA, suggesting that smaller V_max in PVs was due to reduced RMP. Inward rectifier current density in PV cardiomyocytes was ~58% that in LA, potentially accounting for the less negative RMP in PVs. Slow and rapid delayed rectifier currents were greater in PV (by ~60% and ~50% respectively), whereas transient outward K⁺-current and L-type Ca²⁺-current were significantly smaller (by ~25% and ~30% respectively). Na⁺/Ca²⁺-exchange (NCX) current and T-type Ca²⁺-current were not significantly different. In conclusion, PV cardiomyocytes have a discrete distribution of transmembrane ion currents associated with specific action potential properties, with potential implications for understanding PV electrical activity in cardiac arrhythmias.