We sought to determine if changes in myocardial physical properties, detected by ultrasound tissue characterization (UTC), are present in asymptomatic children years after an acute episode of Kawasaki disease (KD) and if such changes are related to coronary artery aneurysms (CAs). Myocardial UTC analysis was performed 4.8 + or - 3.4 years after acute KD in 22 patients, mean age 6.6 + or - 3.4 years, with or without CA, who had a normal ECG and normal left ventricular (LV) systolic and diastolic function by echocardiography. Twenty-two age-matched subjects were studied as controls. Cyclic variation of integrated backscatter (cvIBS) and calibrated integrated backscatter (cIBS) were assessed in 16 LV myocardial segments in each patient and control. We found large differences in the UTC data between patients and controls: cvIBS, 7.8 + or - 0.8 vs 8.9 + or - 0.6 dB; cIBS, 28.6 + or - 3.2 vs 25.2 + or - 1.0 dB (P\10-3 for both). The average values of cIBS and cvIBS did not differ significantly between KD patients with and patients without CA or stenosis. In conclusion, UTC analysis demonstrated significant differences in myocardial tissue properties between KD patients and controls, despite similar measures of LV function, independent of coronary artery abnormalities. UTC analysis might improve risk stratification for KD patients.