 This is a double-blind study that will randomise breast cancer subjects in 1:1 ratio to receive a pecs block of 10 ml of Ropivacaine 3.5 mgml and Clonidine 5 μgml injected between pectoral muscles and 20 ml between the muscles pectoralis minor and serratus anterior arm A versus 10 ml of placebo NaCl 0.9 injected between pectoral muscles and 20 ml between the muscles pectoralis minor and serratus anterior arm B. The pecs block will inject just before the surgery. 