Fildena 25 medicine is a drug like other erectile dysfunction pills with minor side effects, rarely accounted for. Sildenafil citrate is the active ingredient in tablets of fildena which basically works in erectile dysfunction by relaxing the muscles in the penile blood vessels in men and increasing blood flow to the penis. Sildenafil citrate also works by relaxing the blood vessels in the lungs to allow blood to flow more easily in pulmonary hypertension.