I asked this question to a very knowledgable friend who just happened to have a friend who worked in a pharmacy in Athens and his answer was Other contraindications include hypersensitivity to any component of the formulation, pulmonary veno-occlusion, left ventricular outflow obstruction, PAH associated with sickle cell anemia, and multiple system atrophy. Pediatric Patients: Increased mortality with increasing sildenafil dose was observed in a clinical trial of pediatric patients with PAH. Continuing Education Activity Sildenafil is a medication used in the management and treatment of erectile dysfunction and pulmonary arterial hypertension. Sildenafil may not be safe to take for people with certain medical conditions including: a past history of stroke or heart attack in the last 6 months retinitis pigmentosa an eye disease It can also interact with many other medicines, particularly nitrates used in heart disease , amyl nitrite and blood pressure medicines. Often, these are prescribed for chest pain called angina.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. Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. We would like to show you a description here but the site won’t allow more.