Valvular lesions in the acute phase of Kawasaki disease were studied in 19 children. The patients were intensively observed by color flow Doppler every day from the day of hospitalization up to 12 days after the onset of the disease and 2 or more times a week thereafter, for up to 28 days. Mitral regurgitation (MR) was found in 9 patients (47%) and tricuspid regurgitation (TR) in 10 (53%). MRs were of transient type and confirmed from 7.5 +/- 1.6 (mean +/- standard deviation) to 13.1 +/- 6.5 days after the onset of the disease. Both types of valvular regurgitation were mild. The direction of regurgitation was from the center of valvular coaptation toward the posterior wall of the atrium. Neither valvular prolapse nor valvular deformity was noted. In patients with MR, left ventricular ejection fraction on M-mode echocardiography was significantly lower in the acute phase than in the convalescent phase of the disease (p less than 0.05). Using gallium-67 scintigram, the positive uptake of the isotope was noted in 7 (88%) of 8 patients with MR, but not found at all in 8 patients free of MR. These results suggest that MR and TR are often transient in the acute phase of Kawasaki disease and could be attributed to myocarditis.