There is considerable evidence that oxygen free radicals are involved in reperfusion injury of ischemic myocardium. Epidemiologic studies showed an inverse correlation between plasma levels of alpha-tocopherol (vitamin E) and ascorbic acid (vitamin C) and mortality from ischemic heart disease. The present study examines the influence of both vitamins on the toxic effects of singlet oxygen on isolated rat cardiomyocytes. Freshly isolated cardiomyocytes from adult rats were exposed to singlet oxygen which was generated by photoactivation of the photosensitive dye rose bengal (10(-7) M). This procedure induced irreversible hypercontracture in about 95% of rod-shaped cardiomyocytes within 15 min after onset of photoactivation of rose bengal. Pretreatment with vitamin C (10(-5) to 10(-2) M) or E (10(-6) to 10(-3) M) reduced the number of hypercontracted cells after exposure to singlet oxygen in a concentration-dependent manner. Simultaneous application of both vitamins (vitamin E 10(-6) M plus vitamin C 10(-5) M or vitamin E 10(-5) M plus vitamin C 10(-4) M) revealed a marked overadditive protective effect against oxidative damage as compared with the single application of each vitamin. Our data show that alpha-tocopherol and ascorbic acid exert direct protective actions on isolated cardiomyocytes against oxidative damage and provide an overadditive effect if administered simultaneously.