This will increase the supply of blood to the lungs and reduce the workload of the heart. Some medications should not be taken with sildenafil. Although not all of these side effects may occur, if they do occur they may need medical attention. Use only the brand of this medicine that your doctor prescribed. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis. Keep from freezing.Viagra is an effective drug for treating male erectile dysfunction, but it targets sexual performance, not sexual arousal. There is limited evidence that Viagra may be beneficial . US Brand Name Revatio Viagra Descriptions Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of .  · The highest recommended Viagra dose for treating erectile dysfunction (ED) is mg per day, according to the drug’s manufacturer. Doses of mg or mg would be considered off-label use.