Reperfusion- and reoxygenation-induced ventricular tachyarrhythmias were studied on 6-month-old (adult) and 24-month-old (senescent) Langendoríf perfused rat hearts. The incidence of arrhythmias was significantly higher in the group of senescent hearts. Furthermore, the reperfusion- and reoxygenation-induced contracture was also more frequent in the group of senescent hearts. The interrelation between contracture and arrhythmias might represent an indirect evidence to suggest that alterations in cell calcium homeostasis have an important role in the origin of both phenomena and, possibly, in their increased incidence in the senescent heart