PDE5A and pulmonary arterial hypertension: PDE5 inhibitors (PDE5is) such as sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) have proven efficacy in treating erectile dysfunction and pulmonary arterial hypertension (PAH).3 Underlying their utility in both conditions is a well-defined action on the vasculature through enhancement of cGMP derived from nitric oxide (NO), leading to relaxation of vascular smooth muscle and vasodilatation.