(A) Experimental protocol for reversal of pulmonary hypertension showing timing of administration of MSC-EV or PBS vehicle. (B and C) RVSP (B) and RV/LV+S (C) were measured 3 weeks after removal from 3 weeks of hypoxia. *P<0.05, **P<0.01, ***P<0.001, and ****P<0.0001.