A, Original transient outward K+ currents (ITO) and sustained outward currents (ISUS) in atrial cells from a patient in post-CS SR (□) and post-CS AF (■). Superimposed currents evoked by voltage pulses (100 ms, 0.33 Hz, −50 mV holding potential) increasing in 10 mV steps between −40 and +60 mV. B, Histograms of peak (at +60 mV) ITO (left hand panel) and ISUS (right hand panel) densities in cells from patients in post-CS SR (□, n=60-84 cells, 29-44 patients) and post-CS AF (■, n=13-21 cells, 7-9 patients). Values are means±SE. NS=not significant.