In spite of its high prevalence and the huge burden it imposes on health care systems, heart failure is a clinical syndrome that has not yet been defined satisfactorily. In actual practice, diagnosis requires the presence of typical signs and symptoms along with data from complementary tests that indicate definite cardiac dysfunction. In this article we review current concepts of the disease, stages of development, common underlying causes, and the value of different diagnostic tests. Among these tests, measurement of B-type natriuretic peptide has proved useful for population screening and the differential diagnosis of heart failure. This indicator seems to be the ideal link between the large population of patients in whom heart failure is suspected and the subgroup for whom cardiac ultrasound, the most informative test in this disease, is warranted.