Currently, there has been an increased interest globally to identify natural compounds that are pharmacologically potent and have low or no adverse effects for use in preventive medicine. Myocardial infarction is a vital pathological feature resulting in high levels of mortality and morbidity. Left ventricular hypertrophy (LVH), adenosine triphosphatases (ATPases) dysfunction and electrolyte imbalance play a vital role in the pathogenesis of myocardial infarction. This study aims to evaluate the preventive effects of diosmin on LVH, ATPases dysfunction and electrolyte imbalance in isoproterenol induced myocardial infarcted rats. Male albino Wistar rats were pretreated orally with diosmin (10 mg/kg body weight) daily for a period of 10 days. After pretreatment, isoproterenol (100 mg/kg body weight) was injected subcutaneously into the rats twice at an interval of 24 h to induce myocardial infarction. Isoproterenol induced myocardial infarcted rats showed increased LVH, altered levels/ concentrations of serum cardiac troponin-T, heart ATPases, heart sodium ion, calcium ion and potassium ion, and increased myocardial infarct size. Pretreatment with diosmin revealed preventive effects on LVH, and all the above mentioned biochemical parameters evaluated in isoproterenol induced myocardial infarcted rats. The 2, 3, 5-triphenyl tetrazolium chloride staining on myocardial infarct size confirmed the prevention of myocardial infarction. Further, the 1, 1 diphenyl-2- picryl-hydrazyl (DPPH) radical in vitro study revealed a potent DPPH free radical scavenging action of diosmin. Thus, the observed effects of diosmin are due to its antihypertrophic and free radical scavenging activities in isoproterenol induced myocardial infarcted rats.