Vardenafil, the active ingredient in Filitra 40 mg, belongs to a class of drugs known as phosphodiesterase type 5 (PDE5) inhibitors. These medications work by blocking the action of the enzyme phosphodiesterase type 5, which normally breaks down cyclic guanosine monophosphate (cGMP), a substance that regulates blood flow in the penis. By inhibiting PDE5, vardenafil allows cGMP to accumulate and promote the relaxation of blood vessels in the penis, leading to increased blood flow and improved erectile function.