Cardiac mensuration by radiographic frontal cardiac are method was carried out on 21 patent ductus arteriosuspatients, 15 females and 6 males. Formula used in this study is as follows. Frontal cardiac area =3.14/4 × longdiameter x broad diameter Increase of frontal cardiac area in patent ductus ductus arterisus patients seems to beevident but the degree of the cardiomegaly is variable. Comparing to normal data by Choo and Kim, frontal cardiacarea in patent ducuts arteriosus patients in this series is increased in 15.9% to 98.1%. After surgical ligationof the ductus arteriosus, significant decrease of the frontal cardiac area is observed and the average is 12.5%.