In the present study, we aimed to determine the oxidative damage in rat heart tissue induced by ruthenium(II)-NHC (Ru) and gold(I)-NHC (Au) complexes which have anticarcinogenic effects and not used clinically yet. For this purpose, 35 Sprague-Dawley rats were randomly divided into 5 equal groups. In the control group, rats treated with saline, Ru and Au complexes were intraperitoneally given high (10 mg/kg) and low (5 mg/kg) doses as only one administration. The animals were killed, and heart tissues were taken on day 10 of the drug administration for the determination of the biochemical parameters (malondialdehyde, superoxide dismutase, reduced glutathione and catalase levels). It was determined that both Ru and Au complexes treatment significantly caused oxidative damage compared to the control group. Additionally, it was shown that Au treatment caused more adverse effects than Ru treatment. Also, it was clearly found that the occurred effects were generally determined in a dose-dependent manner. In conclusion, when these compounds synthesized for the treatment of cancer were used, they caused oxidative damage in heart tissue. However, Ru complex could be preferred for cancer treatment in terms of user safety.