Isabella asked the doctor how Matteo had managed to survive so far if blood was not properly circulating to his lungs. What structure was allowing some oxygenated blood access to the systemic circuit, thus keeping Matteo alive immediately after birth?

A. Foramen ovale
B. Chordae tendineae
C. Fossa ovalis
D. Pulmonary semilunar valve
E. Interventricular septum

A. Foramen ovale

Explanation:

From the inferior vena cava the blood flows into the right atrium and is shunted directly into the left atrium through an opening called foramen ovale. It is basically a right to left shunt and there is a valve with two flaps that prevent backflow. It thus allows the blood that still escapes to the right ventricle to bypass the pulmonary circulation. Foramen ovale is patent in 20-30% adults. Although it usually remains functionally closed, any abnormality increasing right atrial pressure above left atrial pressure can produce a right to left shunt across patent foramen ovale.