Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. This increased blood flow can cause an erection. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. If you are a Mayo Clinic patient, this could include protected health information. Here are some steps that might help: If you smoke, quit. What will that cost, and will the visit be covered by my insurance? Side effects Side effects of oral ED medicines are often mild.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep . a light-headed feeling, like you might pass out. Common sildenafil side effects may . Follow all directions on your prescription label. Do not take this medicine in larger or .