Vardaxyn In truth, according to Pfizer, the drug's producer, three million tablets of Viagra are sold every 12 months. To placed it in reality, Viagra blocks the  phosphodiesterase, an enzyme that stops the penis' capacity to get hard. When the phosphodiesterase are already treated with the aid of Viagra, the cyclic  guanosine monophosphate can now help you get an erection....