Using Ionescu-Shiley pericardial xenograft (ISPX), mitral and tricuspid valve replacement was performed on 64 cases during a period of time 1980-1984. On 48 of these 64 cases, ISPX was followed up and observed for its secular change using 2-dimensional echocardiography and ultrasonic Doppler method. The results revealed the following: 1) For ISPX at the mitral position, incidence of obvious cuspal hypertrophy or calcification was 5, 31, and 46% for 3, 5, and 6 years, respectively. 2) Including up to fine changes such as only a slight increase of echo brightness, rate of change detection was as high as 15, 28, 52, and 61% for 2, 3, 5, and 6 years, respectively. 3) Maximum velocity at the left ventricular inflow tract was 1.2-1.5 m/s and remained unchanged so long as ISPX has normally been functioning. Once regurgitation occurred, the flow velocity become greater, and those cases in which it reached 2 m/s needed re-placement. 4) Obvious cuspal hypertrophy showed a tendency to occurring mainly at those cusps which were situated anterior (on the side of outflow tract of left ventricle) regardless of the inserting direction of the prosthetic valve. 5) Five ISPXs at the tricuspid position showed no abnormality. Of 64 cases, 6 (9.4%) showed valvular dysfunction, and even those cases which showed no such dysfunction proved to be subjected to cuspal degeneration at a high rate. For prosthetic valve replacement by ISPX, both frequent examinations by means of echocardiography and Doppler method and careful observation of the course are necessary.