To evaluate the effect of coronary artery bypass grafting (CABG) on left ventricular (LV) diastolic function in coronary artery disease (CAD), pulsed Doppler echocardiography was performed in the patients undergoing CABG between February 1991 and March 1993. The patients with non-sinus rhythm, more than 100 heart beats/min, aortic or mitral valvular disease, and perioperative myocardial infarction or left ventricular aneurysm were excluded from this study. CAD group consisted of 24 patients and Control group 17 normal subjects with no evidence of angina nor ischemic findings on electrocardiogram. No significant differences were found in heart rate, mean blood pressure, left atrial dimension and LV ejection fraction in two groups. Pulsed Doppler echocardiographic examinations showed that in comparison with Control group, E/A ratio was decreased (0.72 vs 0.89, p < 0.05) and IRT prolonged (115.9 vs 92.4, p < 0.05) in CAD group. These results indicated impaired diastolic function in CAD patients. In CAD group, echocardiographic study was performed 3 to 4 weeks after CABG. In 16 patients in whom heart rates at the pre- and the postoperative examinations were relatively identical, E/A ratio increased postoperatively from 0.66 to 0.96 (p < 0.001) and IRT and DHT shortened from 115.2 ms to 86.6 ms (p < 0.001) and from 96.3 ms to 82.4 ms (p < 0.05) respectively. In addition, DC increased from 2.04 cm/s2 to 3.02 cm/s2 (p < 0.005) postoperatively. The results indicated that CABG improved LV diastolic function in CAD patients. In summery, this study indicated that impaired LV diastolic filling was found in CAD patients and that CABG improved LV diastolic function in CAD patients.