Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Recent heart or blood vessel problems. You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. To provide you with the most relevant and helpful information, and understand which information is beneficial, we may combine your email and site usage information with other information we have about you. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox.Viagra works by increasing blood flow to your penis, which helps you have and keep an erection. But this drug only works if you’re sexually aroused. Viagra comes as tablets . Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Do not take Viagra more than once per day. Shake the oral suspension (liquid) before you measure . Revatio Viagra Descriptions Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called .