Fildena 100 is a brand of Sildenafil Citrate, a medication commonly prescribed to treat erectile dysfunction by increasing blood flow to the penis, making it easier for men to achieve and maintain an erection. Sildenafil works by inhibiting the enzyme phosphodiesterase type 5 (PDE5), which regulates blood flow in the body. By blocking PDE5, Sildenafil allows for the relaxation of smooth muscle tissues and dilation of blood vessels, improving circulation.