BNP, brain natriuretic peptide, is a member of a family of hormones with natriuretic, diuretic and vasorelaxant activity. It is secreted mostly from the cardiac ventricles, but it is synthetized in the human brain too. Till now measurement of BNP has been valuable in the rapid diagnosis of heart failure. Reports of changes in BNP content in cerebrovascular diseases suggest that BNP plays a role in pathogenesis and pathophysiology of ischemic stroke. BNP is elevated in nearly two thirds of acute stroke patients. This rise is caused inter alia 1) by the sympathetic system activation, which may have toxic effect on the myocardium, leading to myocardial dysfunction and increased secretion of BNP from the damaged heart, and 2) by increased production of BNP by the damaged part of brain. The attempts to find correlation between circulating NT-proBNP concentration and stroke topography, infarct size or severity of neurological deficit do not give unequivocal results. The same applies to prognostic value of BNP concentration during ischemic stroke. Despite the contradictory findings, it is worth continuing this research, because there is an association between cardiac failure and poor prognosis in acute cerebrovascular diseases. Early prognosis of heart failure in ischemic stroke may be useful in the selection of an adequate therapy and may improve prognosis of acute stroke patients.