To determine the evolution of amyloid heart disease, 28 patients with familial amyloid polyneuropathy (FAP) were studied by echocardiography. The incidence and degree of the abnormalities were correlated with the neurologic disabilities, duration of the illness, and age in cross-sectional studies. Serial studies were performed in 12 patients, who were followed for a mean of 27.7 months. At the initial examinations, left ventricular diastolic function was reduced in six patients, while systolic function was preserved in eight. On follow-up there occurred significant increases in ventricular septal wall thickness (from 10.7 + 3.1 to 13.1 + 3.2 mm; p < .01) and posterior wall thickness (from 11.8 2.5 to 13.5 + 2.3 mm; p < .01), and reductions in the E-F slope of the mitral valve (from 64.4 18.8 to 43.9 ± 1 1.0 mm/sec; p < .01), percent fractional shortening (from 36.5 + 9.4% to 28.8 + 8.2%; p < .02), and left ventricular internal diastolic dimension (from 46.2 + 6.1 to 42.4 ± 6.2 mm; p < .001). At the final examinations, marked ventricular hypertrophy was found in three patients, reduced left ventricular diastolic function in all, impaired systolic function in nine, and decreased left ventricular internal dimension in three. In addition, highly refractile myocardial echoes had appeared in two patients, pericardial effusion in three, and valve thickening in two. We conclude that amyloid heart disease in patients with FAP develops slowly but progressively.