To determine whether the SSPN−/− myocardium is more susceptible to acute ischemia-reperfusion (IR) injury and the development of arrhythmias, we subjected ex vivo perfused SSPN+/+ and SSPN−/− hearts to IR injury, according to the schematic shown in Figure 2A. During the reperfusion phase the intrinsic sinus atrial node pacemaker activity can be determined in Langendorff perfused hearts. This evidence concerns the gene SSPN and cardiac arrhythmia.