Forum:Reptilianne Medusa's effect

I have a card named Reptilianne Medusa. When me and my friend dueled, I activated the effect of my Reptilianne Medusa and reduced his monster's attack to zero. After my turn ended he said that the attack of his monster will be back to it's original attack. Please help me because I really wondered if the effect of Reptilianne Medusa is permanent or not.