A 77-year-old man with dyspnoea was suspected to have a decompensatio cordis by the general practitioner. A diuretic was prescribed. Additional radiological and laboratory investigation (e.g. natriuretic peptides and D-dimers) showed pulmonary embolism instead of heart failure. A second patient, a woman aged 79 years, with a history of leukaemic mantle cell lymphoma, was treated with poly-chemotherapy (R-CHOP), after which remission was achieved. Four years later the lymphoma recurred and R-CHOP treatment was started. However this was without success, after which R-CHOP treatment was repeated. Subsequently the patient developed dyspnoea and pneumonia. Following additional radiological and laboratory investigation (e.g. natriuretic peptides) the patient was finally diagnosed with doxorubicin-induced heart failure. Based upon these case studies, the role of brain-natriuretic peptides in the differential diagnostic work-up of dyspnoea is highlighted. Test performance, correlation with disease, monitoring, prognostics, differential diagnostic power, reference values and pitfalls of brain natriuretic peptides are discussed.