Background: Discordant action potential alternans creates large gradients of refractoriness, which is thought to be the mechanism linking T-wave alternans to cardiac arrhythmogenesis. Since intercellular coupling acts to maintain synchronization of repolarization between cells, we hypothesized that intercellular uncoupling, such as during ischemia, would initiate discordant alternans, and that restoration of intercellular coupling by the gap junction opener rotigaptide may provide a novel approach for suppressing arrhythmogenic discordant alternans. Methods and results: Optical mapping was used to record action potentials from ventricular epicardium of Langendorff-perfused guinea pig hearts. Threshold for spatially synchronized (i.e. concordant) alternans and discordant alternans was determined by reducing cycle length step-wise during: 1) baseline; 2) treatment with rotigaptide or vehicle; and 3) global low-flow ischemia + rotigaptide or vehicle. Ischemia reduced the threshold for concordant alternans in both groups from 362±8 to 305±9 bpm (p<0.01) and for discordant alternans from 423±6 to 381±7 bpm (p<0.01). Interestingly, rotigaptide increased the threshold for discordant alternans relative to vehicle both before (438±7 vs. 407±8 bpm, p<0.05) and during (394±7 vs. 364±9 bpm, p<0.05) ischemia. Rotigaptide increased conduction velocity and prevented conduction slowing and dispersion of repolarization during ischemia. Confocal immunofluorescence revealed that total connexin43 quantity and cellular distribution was unchanged before or after low-flow ischemia, with and without rotigaptide. Finally, enhancement of connexin43 dephosphorylation in response to low-flow ischemia was significantly reduced by rotigaptide (15.9±7.0 vs. 0.3±6.4%, p<0.001). Conclusions: These data suggest that intercellular uncoupling plays an important role in the transition from concordant to discordant alternans. By suppressing discordant alternans, repolarization gradients, and connexinx43 dephosphorylation, rotigaptide may protect against ischemia-induced arrhythmias. Drugs that selectively open gap junctions offer a novel strategy for antiarrhythmic therapy.