Viagra (sildenafil) , the world's first oral PDE5 inhibitor (Phosphodiesterase inhibitor) , is used to treat male erectile dysfunction (also known as impotence or Ed) , the treatment of erectile dysfunction (ED) has made revolutionary progress, which can effectively improve erectile stiffness. At any time, patients taking nitrates of any dosage form must not take Viagra at the same time. Including the nitroglycerin. If viagra is used with either nitrates, the patient's blood pressure may suddenly drop to unsafe or life-threatening levels.