Brain natiuretic peptide (BNP) is a hormone secreted specifically by the left ventricular myocytes. Its concentration is correlated with the severity of symptomatic or asymptomatic left ventricular dysfunction. The measurement of BNP has several applications from the screening of populations to the monitoring of the effects of treatment and the evaluation of the prognosis of cardiac failure. The emergence of new methods of rapid measurement will enable its usage as a routine investigation in the near future. Large scale clinical trials are, however, required to confirm the hopes raised by this new marker of left ventricular dysfunction.