These medicines are called PDE5 inhibitors. Recent heart or blood vessel problems. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Medicines that block an enzyme called CYP3A4. This boosts blood flow and helps you get an erection from sexual activity. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. Key facts It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction.How does Viagra work? Viagra is used to treat erectile dysfunction (ED). It decreases ED symptoms by helping you get and keep an erection. Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing .