The length and arrow or the PAS of 130 normal cases were measured, respectively. The BSA (m2) ranged between 0.30--2.05, and the ages between 6 months and 40 years. 2. Seventy-three cases VPS were divided into four groups according to the peak SPRV: Group 1, less than 50 mm Hg; Group 2, from 50--75 mm Hg; Group 3, from 75--150 mm Hg; and Group 4, with more than 150 mm Hg. The length and arrow of the PAS was measured. The age of the patient ranged from 4--38 years. 3. In normal cases, the PAS was a straight line or presented a slight concavity in 30% of the cases. 4. In cases of VPS all of them had a slight or marked bulging of the PAS, except one in Group 1 (6.6%); two in Group 2 (11%); three in Group 3 (10%); and one in Group 4 (8.3%). Marked convexity (more than 10 mm of arrow of this segment) was found one time in Group 1 (6.6%); three times in Group 2 (16%); three times in Group 3 (10%); and twice in Group 4 (16%). 5. In normal cases the length and the arrow of the PAS tend to have greater values when the BSA is higher. When the arrow of the segment is above 5 mm and the length higher than 50 mm, irrespective to the patient's age, we must be facing an abnormal finding and all those diseases capable of giving an abnormal PAS should be considered. 6. We want to stress the importance of obtaining a proper roentgenogram to assess, with accuracy, the quantitative and qualitative data needed to do a correct interpretation of the cardiac silhouette.
