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Evidence is presented which indicates that shunting of small amounts of blood from right to left occurs frequently through interatrial communications. Such right-to-left shunts are of small magnitude in the usual case of atrial septal defect, but it appears that of the fractions of blood shunted, a greater proportion has originated from the inferior vena cava than from the superior vena cava.
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Swan et al. (1954) studied this question.
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