A, Original currents recorded in response to a voltage ramp, increasing from −120 to +50 mV at 24 mV/s, in atrial cells from a patient in post-CS SR (□) and post-CS AF (■). B, Histogram of means±SE inward rectifier K+ current density (IK1, measured at −120 mV) in cells from patients in post-CS SR (□, n=111 cells, 48 patients) and post (7 day)-CS AF (■, n=26 cells, 10 patients). NS=not significant.