Whey protein (WP) is a dietary supplement. It helps bodybuilders and athletes recover faster, reduce excess weight, and enhance muscle mass. The excessive use of such supplements causes substantial stress on your body. Nandrolone decanoate (ND) is a synthetic testosterone derivative that is unconstitutionally abused by young athletes to enhance their physical endurance, despite its severe adverse effects and global restriction. Aim Because we do not know how whey protein and nandrolone affect the cardiac system in supraphysiological doses taken by athletes, our objective is to investigate the cardiac effects of short-term use of whey protein and nandrolone. Methods Thirty adult male albino rats were divided into four groups; control group: fifteen rats were divided into three equal subgroups; (control negative (CN): standard diet and free tap water, control distilled water (CDW): distilled water, and control peanut oil subgroup (CP): peanut oil). Whey protein group (WP): (five rats) WP was given by oral gavage daily except Friday at a dose of 5.4 g/kg. In addition, nandrolone decanoate group (ND): five rats got 36 mg/kg of ND intra-peritoneally once a week. Finally, five rats in the combined group (Comb) were given the exact doses of WP and ND. After four weeks, blood samples were taken from all the animals for further analysis. Moreover, the right and left ventricles were preserved for biochemical and histological study. Results ND and Comb groups had severely deleterious effects on the ventricular muscle, while the WP rats showed considerably mild effects Conclusions As a consequence of these findings, it is recommended that WP should be administered under medical supervision for restricted doses, while ND must be entirely prohibited.