Figure 1. Echographic views centered on right and left atrium without (a) or with (b and c) contrast echoes, in the presence (c) or absence (a and b) of inhaled nitric oxide. LA = left atrium; LV = left ventricule; RA = right atrium; RV = right ventricule. (A) In the absence of nitric oxide, the interatrial septum is curving to the left, suggesting a positive right-to-left pressure gradient. (B) In the absence of nitric oxide, contrast echoes massively move from right to left atrium: There is a right-to-left intracardiac shunt due to the PFO. (C) In the presence of inhaled nitric oxide, microbubbles are no longer seen in the left atrium, indicating a closure of the PFO.