BACKGROUND: Elastic recoil contributes to the residual lumen reduction immediately after PTCA. We evaluated the factors to influence on immediate elastic recoil after the successful PTCA. METHODS: 88 patients(96 lesions) were studied by quantitative angiography. Angiograms were obtained in two identical near orthogonal projection before PTCA and immediately after the last balloon deflation. RESULTS: Immediately after PTCA, minimal luminal diameter increased from 0.7+/-0.6mm to 1.9+/-0.6mm and percent diameter stenosis was reduced from 77+/-20 to 34+/-21%. The calculated mean elastic recoil was 0.5+/-0.7mm in diameter and % elastic recoils were lesser both in calcified(3+/-23 vs 23+/-24%, p=0.04) and thrombotic(9+/-20 vs 23+/-35%, p=0.02) lesions. The elastic recoil increased significantly according to the inflation diameter of balloon(r=0.32, p<0.01. No significant correlation between the immediate elastic recoil and age, sex, risk factors, eccentricity and lesion length was shown. CONCLUSION: The elastic recoil immediately after a successful PTCA was dependent on the existance of calcium and thrombus on the target lesion and on the balloon size at the maximal inflation.