This study was undertaken to evaluate the preventive role of S-allyl cysteine sulphoxide (SACS) in isoproterenol (ISO)-induced cardiotoxicity in male Wistar rats. Myocardial infarction was induced by subcutaneous injection of ISO (150 mg/kg) once a day for 2 days. SACS (40 and 80 mg/kg) was given as pretreatment orally daily for a period of 35 days using an intragastric tube. SACS pretreatment significantly lowered thiobarbituric acid reactive substances (TBARS) and increased the activities of mitochondrial superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione S-transferase (GST), and the concentration of reduced glutathione (GSH) in myocardial infarcted rats. SACS pretreatment also increased significantly the levels of mitochondrial phospholipids and decreased the levels of mitochondrial cholesterol, free fatty acids (FFAs), triglycerides (TGs) and calcium, and the activity of xanthine oxidase (XOD) in heart. Further, the activities of isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), alpha-ketoglutarate dehydrogenase (alpha-KGDH), NADH-dehydrogenase, and cytochrome C-oxidase were significantly elevated in the mitochondrial fraction of the heart in the SACS-pretreated ISO-induced rats. Oral administration of SACS for a period of 35 days to the normal control rats did not show any significant effect. Histopathological studies of the myocardial tissue showed a protective role of SACS in the myocardial-infarcted rats. The effect at a dose of SACS 80 mg/kg was more effective than the dose 40 mg/kg. The results of the study conclude that SACS protect the mitochondria of the ISO-induced myocardial-infarcted rats.