 3. Treatment assignment and randomization if applicable To ensure a robust and unbiased approach, randomization should account for demographic characteristics of the patients i.e.: age, sex and glomerular filtration rate GFR. Only patients who are cared for by experienced anesthesiologists and cardiac surgeons more than 5 years of staff experience will participate in this study. Participating surgeons and anesthesiologists will be allocated to alternating nitric oxide NO vs. nitrogen N2 use. The patients will be randomized to receive either NO study drug or N2 placebo alone. The random allocation sequence will be created using a computerized random generation program. The randomization will be in blocks of 10 patients. This procedure will be performed by an external staff person working in the Critical Care Laboratory of the Department of Anesthesia. Patients will be randomly allocated to one of the test gas study groups 80 ppm NO in N2 or the placebo group N2. The intervention will consist of administering the test gas via the cardiopulmonary bypass CPB machine and after CPB via the inspiratory limb of the anesthetic or ventilator circuit, and thereafter via the mechanical ventilator in the Intensive Care Unit ICU. Test gas administration will commence at the onset of CPB and last for 24 hours or until extubation if this occurs before 24 hours. At the end of 24 hours, inhaled NO iNO will be weaned and discontinued while carefully monitoring hemodynamics for a period of 2-4 hours. Local guidelines for NO gas discontinuation will be followed. Using commercially available tanks of Nitric Oxide Airgas Inc, Radnor Township, Pennsylvania or volumetrically-calibrated flowmeters, pure N2 placebo or 800 ppm NO gas in N2 will be mixed with pure oxygen O2 or air to obtain the desired concentration of O2 and, in the NO treatment group, a final concentration of 80 ppm NO. Nitric oxide, nitrogen dioxide NO2, O2 and methemoglobin Met-Hb levels will be continuously monitored. Patients in the placebo N2 group will receive nitrogen test gas during the same 24 hour-period. The inspired oxygen levels will be maintained at the usual levels required for routine post-operative care. No changes to the usual and customary standards of care for any intraoperative or postoperative treatment will be made during the study period. 