Sonographic images of a 21-gestational-week fetus in which PAVSD was falsely suspected. In the 4CV, a deficiency of the atrial septem primum was suspected by sonographers under Protocol A, as indicated by the white arrows. It was in actuality the echo of the coronary sinus which could be visualized when a non-standard 4CV was obtained with the section across the atrioventricular groove. These specific signs were mentioned in Protocol B