Vascular complications are a leading cause of mortality and morbidity in diabetic patients. Herbal drugs are increasingly being used in the treatment of cardiovascular disorders. The present study was designed to examine the therapeutic potential of Terminalia arjuna bark extract in improving myocardial function in streptozotocin (STZ)-induced diabetic rats. After 8 weeks of STZ administration, rats showed a decline in left ventricular pressure (LVP), maximal rate of rise and fall in LVP (LV [dP/dt] max and LV [dP/dt] min), cardiac contractility index (LV [dP/dt] max/LVP), and rise in LV end-diastolic pressure. Altered lipid profile, oxidative stress, and increased levels of endothelin 1 (ET-1), tumor necrosis factor-α (TNF-α), and interleukin 6 (IL-6) along with histological changes in heart and pancreas were observed in diabetic rats. T arjuna significantly attenuated cardiac dysfunction and myocardial injury in diabetic rats. It also reduced oxidative stress, ET-1, and inflammatory cytokine levels. The decreased body weight, heart rate blood pressure, and raised blood sugar in diabetic rats did not improve after T arjuna therapy. Results suggest that T arjuna bark extract improves the altered myocardial function in diabetic rats possibly through maintaining endogenous antioxidant enzyme activities, decreasing ET-1 and cytokine levels.