PDE5A and pulmonary arterial hypertension: Two main classes of pharmacological agents that increase intracellular concentrations of cGMP via the NO pathway have been approved by the Food and Drug Administration (FDA) and are widely used in medicine: PDE5 inhibitors (e.g., sildenafil and tadalafil), which are used to treat erectile dysfunction and pulmonary arterial hypertension [22], and sGC stimulators (e.g., riociguat and vericiguat), which are used to treat pulmonary arterial hypertension and cardiac failure [23].