At the Department of Thoracic and Cardiovascular Surgery, Hanyang university, from 1976 to 1984, 102 patients operated for isolated patent ductus arteriosus were studied. The correlation between the degree of left ventricular hypertrophy [LVH] and hemodynamic data, and postoperative changes of electrocardiographic findings were evaluated. The following results were obtained; [1] Of 102 patients with isolated patent ductus arteriosus, 78 patients [76.5%] were found to have LVH by EKG, preoperatively. [2] The patients with LVH had higher incidence of respiratory infection [79.4%] compared to patients without LVH. [3] Frequent physical findings in the patients with LVH were precordial bulging and P2 accentuation on auscultation. The typical continuous machinery murmur was not different in two group with or without LVH. [4] 66.1% of patients with LVH showed more than 56% of cardiothoracic ratio [CTR] on simple chest X-ray. 56.5% of patients without LVH showed less than 50% of CTR. [5] In the patients found to have LVH by EKG, the correlation between values of Svl+Rv6 and Qp/Qs in hemodynamic data was correlation coefficient 0.57 and between CTR and Qp/Qs was correlation coefficient 0.51. [6] In patent ductus arteriosus with LVH following surgery, the values of Svl+Rv6 was changed from preoperative 153.6$pm$42.78% to 107.7$pm$19.58% within 3 months and to 80.4$pm$12.22%, which is within normal range of Svl+Rv6 on EKC, after 6 months.