Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. However, if you take sildenafil with a high-fat meal, it will take longer for the medication to start to work. Often, these are prescribed for chest pain called angina. It is not indicated for children. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox.For ED: Sildenafil works by increasing blood flow to the penis. This helps you get or maintain an erection. Sildenafil only works for ED if you’re sexually aroused. . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood .