The roentgenographic studies of 42 cases of single ventricle are presented. The value of the plain roentgenograms was considerably limited as a diagnostic means. Single ventricle was angiocardiographically divided into 3 types. Type I, II and III corresponded to Van Praagh’s Type A, C and B+D, respectively. It was relatively easy to establish diagnosis of Type I, based on recognizing an infundibular chamber connected with the large single left ventricle. Those which had 2 well-developed ventricular structures were considered as Type II. Type III could not be further divided into Type B and D. As a rule, determination of the ventriculotruncal relationship was based not on the relative location of the great arteries, but on the connection of the ventricular structures and the great arteries. According to this rule, Type I and II had several ventriculotruncal relationships and Type III was classified exclusively as the double-outlet right ventricle type. From the surgical standpoint of view, it was very important to establish the location and number of the atrioventricular valves. When these were not disclosed on the selective ventriculograms, atrial injection of the contrast medium was helpful to show the anatomy of the valves. Precise angiographic observation is emphasized to determine the anatomy of single ventricle and its associated anomalies.