Background: Whey protein (WP) is considered an ergogenic aid for athletes to improve muscle performance and recovery after sports. Nandrolone Decanoate (ND) is one of the most popular misused anabolic steroids worldwide among bodybuilders because of their anabolic proprieties and capacity to increase exercise tolerance. Objective: This study aimed to evaluate the possible toxic effects of WP and ND on the heart of adult male albino rats. Methods: Thirty adult male albino rats were divided into four main groups; Control Group: (15 rats) were classified into three equal subgroups: control negative (CN): fed a regular diet and tap water. Control distilled water (CDW): received 2ml/kg/day of distilled water orally. Control peanut oil (CP): received intra-peritoneal peanut oil 0.5 ml/rat once weekly. Whey Protein group (WP):(5 rats) received WP orally at a dose of 5.4g/kg/day. Nandrolone decanoate group (ND):(5 rats) received ND intra-peritoneal at a dose of 36mg/kg once weekly. Combined group (Comb): (5 rats) received WP and ND at the same doses. After eight weeks, all animals were sacrificed, and blood was collected for analysis. The heart was preserved for biochemical and histological examination. Results: WP and ND proved to have significant toxic effects on blood parameters and histopathological changes in the heart. Conclusion: These findings support that the heart is highly sensitive to WP and ND administration, and it is necessitated careful administration of dose and for such period under medical supervision for better health.