Angiocardiographic studies of the Anuran double circulation

Angiocardiography was used to investigate cardiovascular flow patterns in the heart and great vessels of the bullfrog and the marine toad. In the frog, these studies revealed a completely selective distribution of right atrial blood to the pulmocutaneous arches. The selective distribution is affected, in part, by the ventricular trabeculae which maintain in the ventricle a separation of right and left atrial blood, by the sequential movement from the ventricle of first right and then left atrial blood, and by a sphincter‐action at the point of division of the truncus arteriosus which effectively shunts right atrial blood into the pulmocutaneous circuit. Left atrial blood in the frog is initially distributed selectively to the systemic arches; late in ventricular systole, some left atrial blood enters the pulmonary circuit. In the toad, both left‐to‐right and right‐to‐left mixing appear to occur, but only after significant periods of selective distribution.