A. Apical four-chamber view on transthoracic echocardiography performed before atrioseptostomy (veno-arterial ECMO flow = 1.5 L/min). The view showed a dilated right ventricle, a compressed D-shape left ventricle, and a flattened septum. B. Transthoracic echocardiography with Color Doppler. A turbulent blood flow is visible through the interauricular septum. The flow appears bidirectional (with both blue and red signals mixed). The peak velocity is indicated around 47 cm/s, with a color scale ranging from −31 to +47 cm/s. C. Transthoracic echocardiography with a bubble contrast study. The bubble contrast study shows an opacification of the right-sided chambers and an immediate left heart opacification, suggesting an overt shunt.