Figure 1. Original raw traces of contraction force (tension, g) of representative experiments conducted on (A) young and (B) middle-aged rats. Arrhythmias were produced by 15-min occlusion of the left anterior descending coronary artery in isolated rat hearts followed by reperfusion for 30 min. Insets demonstrate ventricular fibrillation during the reperfusion period. Arrhythmia severity index (ASI) = 12 for the young rat and ASI = 4 for the middle-aged rat.