Angiotensin II (Ang) stimulation as well as hyperglycaemia (HG), a common risk factor for diabetes, increase formation of reactive oxygen species (ROS) via NAD(P)H-oxidase in adult ventricular cardiomyocytes. The aim of the present study was to determine the role of oxidative stress caused by either Ang, HG or a combination of both on contractile function of cardiomycytes. Freshly isolated cardiomoyctes were incubated with Ang (1–100 nM), HG (15 mM), or a combination of both substances for 24 h. Parameters of contractile function were examined at 0.5 to 2.0 Hz via a line camera. ROS formation was determined via measurement of DCF-fluorescence. Ang increased formation of radicals at a concentration of 100 nM. At that concentration Ang also leads to a reduction of contractile function (-7.4%, -9.3%, and -13.7% at 0.5, 1.0, and 2.0 Hz). HG leads analogically to an increased formation of ROS and a more pronounced decrease in contractile function at higher frequency ranges. A combination of both did not cause an additive effect. Inhibition of ROS production with BMS-191563, a farnesyltransferase inhibitor, reduced the negative effect on contractile function by Ang. Chronic exposure of cardiomyocytes to Ang or HG negatively affect contractile function in a redox-sensitive way. Other, non redox-sensitive, signalling mechanisms by Ang seems to have opposite effects.