So take comfort in knowing that you are not alone. Erectile dysfunction impotence is the inability to get and keep an erection firm enough for sex. If you have persistent trouble getting or keeping an erection, you might have erectile dysfunction. Sexual arousal is a complicated process. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. Rarely reported side effects include: an erection that will not go away priapism.What is sildenafil? Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, which is only. You shouldn’t take Viagra if you’re younger than 18 years. This is because the safety and effectiveness of Viagra haven’t been studied in people of this age group. Viagra and . For erectile dysfunction, the drug must be taken only as required, preferably 30 minutes before the act. DO NOT take more than two doses in a day. The recommended dose for .