Viagra is one of a class of drugs known as PDE-5 (Phosphodiesterase type 5) inhibitors. Viagra and the other PDE-5 inhibitors can help men with erectile dysfunction (male impotence) by enhancing the erectile response when a man is sexually stimulated.Aside from Viagra, the other drugs in this class are Cialis (Tadalafil) and Levitra (Vardenafil).iagra and the other PDE-5 inhibitors can help men with erectile dysfunction (male impotence) by enhancing the erectile response when a man is sexually stimulated. Aside from Viagra, the other drugs in this class are Cialis (Tadalafil) and Levitra (Vardenafil).