Diastolic dysfunction is often the earliest manifestation of diabetic cardiomyopathy, usually accompanied by adverse cardiac remodeling and increased oxidative stress. We tested the hypothesis that administration of Coenzyme Q10 (CoQ) attenuates type 1 diabetes-induced left ventricular (LV) dysfunction and remodeling. Further, we aimed to compare the efficacy of CoQ to the ACEI, ramipril. Male 6-week old mice received either streptozotocin (STZ, 55mg/kg/day for 5 days) to induce diabetes, or citrate buffer. After 4 weeks, mice were treated with either CoQ dissolved in olive oil (10mg/kg/day), olive oil alone, ramipril (3mg/kg/day) or left untreated for 8 weeks (n=11-14/group). Diabetic mice had increased blood glucose levels compared with non-diabetic controls. Superoxide (O2-) production was enhanced in untreated diabetic mice, and attenuated with CoQ treatment. Diastolic function was impaired in diabetic mice, on Doppler echocardiography (E/A ratio, deceleration time DT) and catheterization (LV end diastolic pressure EDP and LV–dP/dt). Administration of CoQ ameliorated diastolic dysfunction on E/A ratio, DT and LVEDP in diabetic mice, with a similar trend on LV-dP/dt. Although DT and LVEDP were improved with ramipril treatment, E/A ratio was not. Diabetic mice also exhibited cardiomyocyte hypertrophy (H&E staining), cardiac fibrosis (Sirius red staining) and increased apoptosis. Both CoQ and ramipril reduced these markers of adverse LV remodeling. In conclusion, these data suggest that both CoQ and ramipril can attenuate diabetic cardiomyopathy. Addition of CoQ to standard care may offer improved treatment of diastolic dysfunction in diabetic patients.