There is a correlation between supply and demand imbalance of oxygen at the tissue level with central venous blood gas parameters in blood in cardiac surgery patients, however current evidence is inconclusive. Objective: To evaluate the usefulness of venous gases as prognostic marker of major postoperative complications in cardiac surgery patients. Methods: Analytical observa-tional prospective cohort study in patients undergoing cardiac surgery scheduled, admitted to ICU, ≥ 18 years. Postoperative venous repeated measurements were performed gases. Results: 55 patients were included in this study. There were no baseline demographic differences between patients who developed major complications (CM) and those without (NCM). CM patients had longer times of CPB and aortic clamping, need for blood products, vasoactive and reoperations in ICU than NCM group. PH values at admission to ICU < 7.315, ScvO2 < 67% at admission and < 65% at 6 hours after admission to ICU identify patients who may have adverse events during the 30 days after surgery. Conclusions: pH levels at admission, central venous saturation ICU admission and 6 hours after surgery and blood sugar immediately after cardiac surgery are independent prognostic markers for major complications, including death.