Seventy patients with rheumatic valvular disease were evaluated with preoperative CT scanning. The correlation of the obtained CT images to the operative findings were examined. Left atrial thrombi were found in 24 cases at the operation. CT scan had detected thrombi in 19 cases (79.2%) and echocardiography in 15 (62.5%). CT failed to find them in 5 cases in which the left atrial thrombi were less than 3g. Echocardiogram, however, failed to detect thrombi in 9 cases, the largest being 14g. There were 15 cases with left atrial calcification, in which 10 cases had left atrial thrombi. Nine cases out of these 10 cases had rough left atrial surface after thrombectomy. Early postoperative CT of 10 with left atrial calcification showed recurrent left atrial thrombi in 4 (40%) cases. Mitral valve calcification was found in 42 cases during operation. CT scan was able to detect it in 40 (95.2%), while echocardiogram detected in 34 cases (81.0%) (p<0.05). All mitral valves with calcification required replacement. Out of 30 cases with non calcified mitral valves, 9 underwent OMC, and the other 21 underwent mitral valve replacement. Aortic valve calcification was found in 9 out of 11 cases with aortic stenosis. All has been diagnosed by CT scan. In conclusion, 1. In detecting the left atrial thrombi, CT scan was superior to echo-cardiography, and provided useful information for planning the operative procedure including atrial approach and valvular manipulation. 2. CT scan could detect calcification of left atrial wall which had high incidence of thrombus formation and rough left atrial surface. 3. CT scan could detect calcification of both mitral and aortic valve, and showed the severity of valvular structural changes.