N-terminal prohormone brain natriuretic peptide (NT Pro BNP) is a sensitive marker of left ventricular function in patients with heart failure. The influence of carvedilol on NT Pro BNP plasma levels was analyzed in 21 heart failure patients. Blood samples were taken before administration and after 12 months of treatment with low-dose carvedilol. Peak oxygen consumption did not change after carvedilol treatment, left ventricular ejection fraction improved (P < .005) in 11 patients (52%), did not change in 9 (43%), and decreased in 1 (5%). In patients where left ventricular ejection fraction improved, NT Pro BNP tended to decrease; however, in patients without improvement, NT Pro BNP increased at follow-up. A correlation exists between magnitude of change in BNP and magnitude of improvement in ventricular function during carvedilol therapy. Patients without noticeable changes in left ventricular ejection fraction with a low to moderate carvedilol dosage show an increase in NT Pro BNP plasma levels.