Both sildenafil and the metabolite have terminal half lives of about 4 hours. In addition, patients were asked a global efficacy question and an optional partner questionnaire was administered. The combination can cause a dangerous fall in your blood pressure. Sildenafil for pulmonary hypertension can also be known by the brand names Revatio and Grandipam. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. For erectile dysfunction, it’s best to take sildenafil on an empty stomach. Its effects might last longer if you have mild to moderate ED.Tell all your healthcare providers that you take VIAGRA. If you need emergency medical care for a heart problem, it will be important for your healthcare provider to know when you last took VIAGRA. Stop sexual activity and get medical help right away if you get symptoms such as chest pain, dizziness, or nausea during sex. Erectile dysfunction is when a man has difficulty getting an erection or keeping it long enough for sex. It’s also known as ED or impotence. It happens when not enough blood flows to the penis, preventing an erection. The frequency increases with age, affecting about 50% of men over age 40*; however younger men may also experience ED. Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work.