Cardiovascular alterations can be improved by the long-term use of fish oil (FO), as well as an adequate supply of copper (Cu). Recently, copper nanoparticles (CuNPs), as an alternative to ionic forms (CuCO3) were found to decrease the level of protein/DNA oxidation. Male Wistar rats were supplemented for 8 weeks with FO (7 g/kg) together with 40 nm sized CuNPs and CuCO3 (6.5 mg Cu/kg). FO with CuNPs modified the superoxide dismutase, catalase, and decreased Cu concentration in the blood. Meanwhile noradrenaline-induced contraction of an isolated aorta was not altered, but acetylcholine-induced vasodilation was reduced. FO with CuCO3 increased the antioxidant capacity of blood, and Zn concentration, however decreased the level of triglycerides. Noradrenaline-induced contraction was improved with no change in acetylcholine-induced response. Since the modifications induced by the FO-supplemented diet corresponded with different Cu formulations, the interaction between FO and CuNPs may follow the replacement of CuCO3 with CuNPs.