Phosphodiesterase type 5 inhibitors increase the intracellular level of cyclic guanosine monophosphate that is a potent nitric oxide dependent vasodilatation and antiproliferation agent. Unlike vardenafil and tadalafil which are prescribed in the erectile dysfunction, sildenafil is also used in a treatment of the pulmonary arterial hypertension, both congenital and acquired. The drug administration may let to various side effects such epistaxis, headache, flushing, eye problem including blurry vision, retinal hemorrhage and nonarteritic anterior ischemic optic neuropathy. It may be also complicated by high reduction of blood pressure and syncope especially in patients concomitantly treated with oral nitrate medications. High caution should be also taken in patients with a heart failure.