Pulmonary arterial hypertension (PAH) is a devastating disease affecting lung vasculature. The pulmonary arteries become occluded due to increased proliferation and suppressed apoptosis of the pulmonary artery smooth muscle cells (PASMCs) within the vascular wall. It was recently shown that DNA damage could trigger this phenotype by upregulating poly(ADP-ribose)polymerase 1 (PARP-1) expression, although the exact mechanism remains unclear. In silico analyses and studies in cancer demonstrated that microRNA miR-223 targets PARP-1. We thus hypothesized that miR-223 downregulation triggers PARP-1 overexpression, as well as the proliferation/apoptosis imbalance observed in PAH. We provide evidence that miR-223 is downregulated in human PAH lungs, distal PAs, and isolated PASMCs. Furthermore, using a gain and loss of function approach, we showed that increased hypoxia-inducible factor 1α, which is observed in PAH, triggers this decrease in miR-223 expression and subsequent overexpression of PARP-1 allowing PAH-PASMC proliferation and resistance to apoptosis. Finally, we demonstrated that restoring the expression of miR-223 in lungs of rats with monocrotaline-induced PAH reversed established PAH and provided beneficial effects on vascular remodeling, pulmonary resistance, right ventricle hypertrophy, and survival. We provide evidence that miR-223 downregulation in PAH plays an important role in numerous pathways implicated in the disease and restoring its expression is able to reverse PAH.