PDE5A and pulmonary arterial hypertension: PDE5 inhibitors including sildenafil (Viagra®), tadalafil (Cialis®), vardenafil (Levitra®), and avanafil (Stendra®) are commonly prescribed for erectile dysfunction and pulmonary arterial hypertension, where they act by blocking the degradation of cyclic guanosine monophosphate (cGMP), leading to increases in nitric oxide (NO) mediated signalling, causing vasodilation and smooth muscle relaxation [14].