Fildena 40 is a medication commonly used to treat erectile dysfunction (ED) in men. It contains 40 mg of sildenafil citrate, which is the same active ingredient found in Viagra. Sildenafil works by increasing blood flow to the penis, helping achieve and maintain an erection during sexual arousal.it's taken about 30 minutes to an hour before sexual activity. It’s important not to take more than one dose within 24 hours. Common side effects include headaches, flushing, indigestion, nasal congestion, and dizziness. Serious side effects are less common but can include sudden vision loss or an erection lasting more than 4 hours (priapism).