Abstract It is well established that cardiomyopathy is a consistent feature of diabetes and that alcohol consumption increases the risk of cardiovascular disease among diabetic subjects. Acetaldehyde (ACA), the main ethanol metabolite, is considered to play a role in the ethanol-induced cardiac dysfunction. It has been reported recently that the negative inotropic effect of ACA was more potent in the diabetic myocardium. To determine whether the disparate ACA-induced myocardial depression in diabetes is due to intrinsic alterations at the cellular level, mechanical properties in response to ACA were evaluated in ventricular myocytes from both normal and streptozotocin-induced diabetic rat hearts. Myocytes were electrically stimulated to contract at 0.5 Hz and contractile properties analyzed included peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocities of shortening and relengthening (±dL/dt). Ca2+ transients were measured as fura-2 fluorescence intensity (ΔFFI) changes. ACA (0.1–30 mM) disproportionately depressed PS in a dose-dependent manner, in myocytes from diabetic hearts compared to normal hearts. Interestingly, the degree of inhibition in ΔFFI was similar in both groups. Neither the duration nor maximal velocities of shortening and relengthening were affected by ACA in either group. These results are the first to suggest that enhanced ACA-induced myocardial depression in diabetes is due to disparate intrinsic actions on individual myocytes. The mechanism underlying the alteration of ACA-induced myocardial depression may be due, in part, to depressed Ca2+ responsiveness in diabetic hearts.