Background: The oxidative stress is a potent tool of myocardial injury having a special significance during open-heart surgery. Obtaining of hypothermic cardioplegia is based on the decrease of myocard’s metabolic efficiency which results in the increase of its resistance to ischemia. Material and methods: This article is aimed at the evaluation of main indices belonging to oxidative stress in venous coronary sinus blood in 60 patients exposed to valvulopathy correction using hypothermic and normothermic cardioplegia. The patients were divided into 2 groups, depending on cardioplegia: group 1 comprised 30 patients that were subjected to blood hypothermic cardioplagia (t <33ºC); group 2 also consisted of 30 patients, subjected to blood normothermic cardioplegia (t ≥ 33ºC). The groups were homogenous considering clinical and functional indices of the heart, detected with the patients before the surgical intervention. Results: The oxidative stress is found to be activated in open-heart surgery evidence proved by serum lipid hydroperoxides (LH) and malonic dialdehyde(MD) significant increase across 110 min of ischemia and at 2-3 min of reperfusion till 55.7-58.9%. This enhancement is associated with antioxidant system failure due to a significant quantitative reducing of the main antioxidant compounds at 55 and 110 min of ischemia, gluthation-peroxidase, gluthation-reductase, superoxide-dismutase (SOD), catalase (CAT) and total antioxidant activity (TAA) the most marked decline being characteristic to SOD and CAT (41.85-46.20%). However TAA and CAT have elevated in reperfusion start by 14.4 and 32.6%. Conclusions: The normothermic cardioplegia was appreciated as a more favorable condition concerning myocardial antioxidant protection ensuring because it provided a less rise of LH and MD as well as a less depletion of explored antioxidant factors.