To correlate clinical and laboratory variables in carcinoid heart disease, clinical data, echocardiograms, 24-hour urinary 5-hydroxyindoleacetic acid levels and liver function tests were evaluated in 30 patients with the carcinoid syndrome. The dominant cardiac lesion of carcinoid heart disease by echocardiography and Doppler was severe tricuspid regurgitation with right ventricular volume overload. A characteristic finding was thickened, retracted tricuspid valve leaflets that were fixed in a partially open position. Carcinoid heart disease was progressive and often fatal. The 17 patients with echocardiographic evidence of carcinoid heart disease had higher peak levels of urinary 5-hydroxyindoleacetic acid (331 +/- 231 vs 58 +/- 78 mg, p less than 0.001) and more severe hepatic dysfunction than the 13 patients without carcinoid heart disease. Although duration of symptoms of the carcinoid syndrome before echocardiography was similar for patients with and without carcinoid heart disease (5.4 +/- 6.4 vs 6.2 +/- 5.9 years, respectively, p greater than 0.1), survival after echocardiography was shorter for those with carcinoid heart disease (1.9 +/- 1.4 vs 3.8 +/- 2.9 years, p = 0.05). The findings support the concept that long-term exposure of the endocardium to serotonin in the right side of the heart leads to the development of heart lesions; in addition, progressive hepatic dysfunction may allow more serotonin to bypass liver enzymes and reach the right side of the heart.