It was analyzed the causes of respiratory failure in 152 patients who underwent heart surgery. The main group included 19 (12.5%) patients requiring prolonged mechanical ventilation. It was found that in comparison with patients without respiratory failure they had larger volume of the right atrium (97.1±57.1 vs. 45.6±18.3 ml) and pulmonary artery pressure rate (59.2±27.6 vs. 45.6±18.3 mm Hg); vital capacity of lungs was significantly reduced (78.4±24.3 vs. 90.5±18.7%) and FEV1 (74.5±28.4 vs 87.7±19.9%), moreover they had older age. Longer duration of cardiopulmonary bypass (149.6±76.6 vs 119.4±47.3 min) and myocardial ischemia (115.3±53.2 vs 91.9±36.3 min) also were noted in the main group. Encephalopathy has been developed significantly more frequent in these patients (57.9% vs. 1.5%), and there was higher mortality (42.1% vs. 0) in comparison with the control group. It is noted that preoperative reduction of lungs vital capacity to 80% increases incidence of complications. It is evaluated the causes of postoperative exudative pleurisy. Postoperative minimal levels of serum total protein (60 g/l) and albumin (34 g/l) after surgery were defined as predictors of 3 times increasing of hydrothorax.