Sudden death syndrome (SDS) is one of the most serious diseases of fast-growing broilers. The incidence of SDS may result from a decrease in ventricular function. The purpose of this study was to explore the mechanism of sexual difference in the sensitivity of broilers to SDS by measuring their ventricular vulnerability, serum enzyme activities, and serum electrolyte levels. Results were as follows. 1) Ventricular fibrillation thresholds induced by injection of KCl and by electrical stimulus of male broilers were both significantly lower than those of female broilers (P < 0.05), suggesting that the ventricular vulnerability of male broilers was higher than that of female broilers. 2) Serum lactate dehydrogenase and creatine kinase activities of male broilers were significantly higher than those of female broilers (P < 0.01), but there was not a significant difference in serum aspartate aminotransferase activity between male and female broilers. 3) No significant difference was observed in serum electrolyte levels of potassium, sodium, and chloride between males and females. From these results, we concluded that there is a significant difference between males and females in their ventricular vulnerability and serum enzyme activities, which may result in a higher sensitivity of male broilers to injury of the myocardium by stress and may further result in a sexual difference in sensitivity to SDS.