NPPB and atrial fibrillation: The obtained results indicate that the overloaded myocardium in a patient with severe valvular heart disease, expressed by elevated preoperative NT-proBNP values as well as the presence of atrial fibrillation, is particularly sensitive to non-physiological perioperative conditions related to the use of extracorporeal circulation, cardioplegia or blood loss in the perioperative period, which may ultimately lead to cardiovascular failure in the early postoperative period.