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We studied the ratio of the foramen ovale area to the total atrial septum area in 18 normal hearts and 33 hearts with congenital cardiac anomalies. The congenital defects included tricuspid atresia, 5; pulmonary atresia, 4; secundum atrial septal defect, 9; coarctation of the aorta, 8; and aortic stenosis, 7. In the 10% formalin fixed specimens, the margins of the atrial septum were defined and marked with India ink. The hearts were coded, positioned with the septum flat and photographed with a grid. The areas of the atrial septum and foramen ovale were measured using standard planimetric techniques. A ratio of the foramen ovale to atrial septal area was calculated. The area of the atrial septum did not differ significantly among the six groups. The foramen ovale/atrial septal ratio in normal hearts was 0.19 ± .01 (SEM). The ratios in tricuspid atresia (0.41 ± .02), pulmonary atresia (0.38 ± .02), and secundum atrial septal defect (.37 ± .01) were significantly larger than normal (p

Foramen ovale atrial septal ratio in-utero is directly proportional to transatrial blood flow. We now studied FO:AS in defects with VSD or intact ventricular septum (IVS) to ascertain patterns of intracardiac blood flow. Included were 11 normal hearts, 12 isolated perimembranous VSD, 8 coarctation of the aorta (COA) IVS, 10 COA with VSD, 6 type B interrupted aortic arch (IAA), 4 pulmonary atresia IVS, 7 pulmonary atresia VSD, and 10 tetralogy of Fallot. From planimeter measurements of atrial septal and foramen ovale area, we calculated FO:AS. These data presented as x±SD were analyzed by ANOVA. The area of the atrial septum was similar among the groups. FO:AS ratio were: normal heart .24±.07; isolated VSD, .40±.06; COA IVS, .15±.07; COA VSD, .34±.07; IAA, .36±.12; pulmonary atresia IVS, .38±.10; pulmonary atresia VSD, .11±.08; tetralogy of Fallot .19±.06. Thus, defects with intact ventricular septum are associated with a predictable variation in FO:AS ratio suggesting that hemodynamics are an important pathogenetic mechanism in these defects. Conversely, defects with VSD have a discordant FO:AS ratio suggesting that other mechanisms such abnormal conotruncal septation maybe the primary abnoramlity. These results emphasize the defects classified by anatomic similarities may have different pathogenic mechanisms.