(1) Background: The aim of this study was to show the effects of swimming and nandrolone administration on cardiodynamic and morphometric parameters of the isolated rat heart. (2) The study included 72 Wistar rats, divided into three groups, scheduled to be sacrificed after the second, third, and fourth week. Each group was divided into four subgroups: control (T-N-), nandrolone (T-N+), swimming training (T+N-), and swimming training plus nandrolone (T+N+) group. The rats from T+N- and T+N+ swam 1 h/day, 5 days/week while ones from T-N+ and T+N+ received weekly nandrolone decanoate (20 mg/kg). The isolated hearts were perfused according to the Langendorff technique and measured parameters: dp/dt max/min, SLVP, DLVP, heart rate, and coronary flow. Hearts were fixed and stained with H/E and Masson trichrome dyes. (3) dp/dt max and dp/dt min were increased in the T-N+ group at higher perfusion pressure compared to the T-N- group. SLVP and DLVP were increased in all groups after the 4th week. Collagen content was increased in T-N+ by 403% and in T+N+ by 357% groups, while it was decreased in T+N- compared to the control after 4th week. (4) Conclusions: Nandrolone alone or combined with swimming had a deleterious effect on myocardial function and perfusion.