The present study was designed to investigate and compare the effects of dietary antioxidants on the mechanical and electrophysiological characteristics of the rat heart. Both sex weanling rats were fed a standardized selenium (Se) and vitamin E deficient diet (GI). or a Se excess diet (GII), or a control diet (GIII). In vitro papillary muscle and Langendorff perfused heart functions of GI and GII did reveal impaired contractile performance and increased heart rate and coronary perfussion pressure. The L-type calcium current (ICa) was investigated in GI, GII and GIII rat ventricular myocytes as a possible cause of cardiac dysfunction. The ICa and current densities measured in GI and GII heart cells (1.4±0.6nA and 8.9±2.8pA/pF; 1.6±.7nA and 8.6±3.2pA/pF) were not significantly different from the values of GIII cells (1.3±0.5nA and 7.0±2.5pA/pF). When expressed as a %, the maximal increase in the peak contractile force of papillary muscle and ICa amplitude that was obtained with 1 mM isoproterenol (ISO) were less in GI and GII (26% and 20%; 34% and 30%) than in GIII (80% and 90%). The voltage and time dependence of ICa in GI and GII showed some significant alterations. Stimulation of ICa, by ISO was decreased in agreement with a reduced number of binding sites of β-agonists and/or an altered secondary intracellular mechanisms. In conclusion, our data has shown that the diet antioxidants levels are important for maintenance of cardiac functions.