BACKGROUND The association between malignant midgut carcinoid tumours and right-sided cardiac lesions is well known, but the pathogenetic link between tumour secretion and valvular disease is still obscure. The purpose of this investigation was to describe the morphological and functional changes of valvular heart disease in a large patient series and to correlate these findings with hormonal secretion and prognosis. METHODS Of 64 consecutive patients with the midgut carcinoid syndrome followed between 1985 and 1998, valvular heart disease was evaluated in 52 patients by two-dimensional echocardiography, Doppler estimation of valvular regurgitation and flow profiles. A majority was also evaluated with exercise electrocardiography and spirometry. RESULTS Structural and functional abnormalities of the tricuspid valve were found in 65 per cent of patients, while only 19 per cent had pulmonary valve regurgitation. Long-term survival was related to excessive urinary excretion of 5-hydroxyindole acetic acid of over 500 micromol in 24 h, but the main predictor of prognosis was the presence of severe structural and functional abnormalities of the tricuspid valve. Although advanced tricuspid abnormalities were prevalent in this series, only one patient died from right ventricular heart failure. CONCLUSIONS Tricuspid valvular disease is a common manifestation of the midgut carcinoid syndrome and advanced changes are associated with poor long-term survival. Active surgical and medical therapy of the tumour disease reduced the hormonal secretion and, combined with cardiological surveillance, made right ventricular heart failure a rare cause of death in these patients.