Fildena 150 mg contains sildenafil citrate, a PDE5 inhibitor. Sildenafil helps increase blood flow to the penis by relaxing the blood vessels, allowing for better circulation when a man is sexually stimulated. This leads to an erection. The effects of Fildena 150 mg usually last for about 4 to 6 hours, similar to other sildenafil-based medications. This provides a window of time during which sexual activity can occur.