The supine anterior-posterior (AP) view of the chest with a F.F.D. of 40 inches is usually obtained in seriouspatient who is unable to stand upright. It is very important clinically to evaluate cardiac size in such seriouslyill cases, but is often difficult to determine whether the heartis actually enlarged or not on the supine AP viewbecause no standard criteria has not been established yet unlike on the PA view. Present study was carried out todetermine the normal values of cardiac transverse diameter and cardiothoracic ratio(CTR) on the supine AP view,and they were correlated to the values of the PA view. The materials consist of 165 normal Korean adults. Botherect PA view with a F.F.D. of 72 inches and supine AP view with a F.F,D. of 40 inches were taken for each cases.The results obtained were as follows. 1. The internal thoracic diameter was 30.5±1.8cm in male and 27.7±1.5cm infemale on PA view, and 32.4±2.0cm and 29.9±1.6cm respectively on AP view. 2. The cardiac transverse diameter was12.9±1.2cm in male and 12.31±1.0cm in female on PA view, and 15.8±1.3cm and 14.6±1.0cm respectively on APview. 3. The cardiac transverse diameters were correlated between PA view(X) and AP view(Y) with an equation ofY=4.7+0.865 X in male, and Y=4.4+0.863 X in female. 4. The CTR was 0.430±0.041 in male and 0.444±0.035 in femaleon PA view, and 0.490±0.036 and 0.497±0.038 respectively on AP view.