Abstract: It was studied the mitochondrial parameters that characterized the mitochondrial cardiac energy metabolism after one treatment with benzonidazole-Rochagan®. The drug was given orally (100 mg benzonidazole/kg body weight) adult male Sprague-Dawley rats during nine consecutive days. The assayed mitochondrial parameters, using glutamate/malate and succinate as oxidative substrates, were the state 4, the state 3, the respiratory control, the efficiency of oxidative phosphorylation, the transmembrane electrical potential and the activity of the mitochondrial ATPsynthase. The results showed that all these mitochondrial parameters were not altered statistically after the above mentioned treatment, indicating that after this benzonidazole administration the mitochondrial cardiac energy metabolism was not altered.