A decade has passed since the discovery of angiotensin-converting enzyme 2 (ACE2), a component of the ACE2-angiotensin (Ang)-(1-7)-Mas counterregulatory axis of the renin angiotensin system (RAS). ACE2 is considered an endogenous regulator of the vasoconstrictive, proliferative, fibrotic, and proinflammatory effects of the ACE-Ang II-angiotensin II type 1 receptor (AT(1)R) axis. Both animal and clinical studies have emerged to define a role for ACE2 in pulmonary arterial hypertension (PAH). There is scientific evidence supporting the concept that ACE2 maintains the RAS balance and plays a protective role in PAH. The activation of pulmonary ACE2 could influence the pathogenesis of PAH and serve as a novel therapeutic target in PAH. Current therapeutic strategies and interventions have limited success, and PAH remains a fatal disease. Thus, more research that establishes the novel therapeutic potential and defines the mechanism of the ACE2-Ang-(1-7)-Mas counterregulatory axis in PAH is needed.