Diabetes mellitus (DM) is associated with characteristic structural and functional changes of the myocardium, termed diabetic cardiomyopathy. As a distinct entity independent of coronary atherosclerosis, diabetic cardiomyopathy is an increasingly recognized cause of heart failure. A detailed understanding of diabetic cardiac dysfunction, using relevant animal models, is required for effective prevention and treatment of cardiovascular complications in diabetic patients. We investigated and compared cardiac performance in rat models of type-1 (streptozotocin-induced) and type-2 (ZDF) DM using a pressure-volume (PV) conductance catheter system. Left ventricular (LV) systolic and diastolic function was evaluated in vivo at different preloads, including slope of end-systolic (ESPVR) and end-diastolic PV relationship (EDPVR), preload-recruitable stroke work (PRSW), maximal slope of systolic pressure increment (dP/dt_max) and its relation to end-diastolic volume (dP/dt_max-EDV), as well as time constant of LV relaxation, and maximal slope of diastolic pressure decrement. Type-1 DM was associated with decreased LV systolic pressure, dP/dt_max, slope of ESPVR and dP/dt_max-EDV, PRSW, ejection fraction, cardiac and stroke work indexes, indicating marked systolic dysfunction. In type-2-diabetic rats, systolic indexes were altered only to a lower extent, and increase of LV stiffness was more pronounced, as indicated by higher slopes of EDPVR. Our data suggest that DM is characterized by decreased systolic performance and delayed relaxation (mainly in type-1 DM), accompanied by increased diastolic stiffness of the heart (more remarkably in type-2 DM). Based on the sophisticated method of PV analysis, different characteristics of type-1- and type-2-diabetic cardiac dysfunction can be demonstrated.