Breast cancer is the malignant neoplasm with the highest incidence in women in Brazil, with the exception of non-melanoma skin tumors. Breast cancer surgery is an important part of treatment and post-operative pain needs to be adequately prevented and treated. This prospective, randomized, double-blind clinical study aims to evaluate the efficacy of interfascial pectoral nerve block (PECS II) compared to local anesthetic infiltration at the surgical site in patients undergoing breast cancer surgery in terms of pain and nausea. Data collection will be carried out at the Nossa Senhora das Dores Hospital with 133 patients, who will be divided into two groups: the PEC group will undergo PECS II blockade and the LOC group will undergo local anesthetic infiltration at the surgical site. Both interventions will be performed after the induction of opioid-free/sparing balanced general anesthesia. At the end of surgery, the patients will be taken to the post-anesthetic recovery room (PACU), where post-operative pain will be monitored on arrival and at 30-minute intervals up to two hours after surgery, and before the patient is discharged the following day. A visual analog scale (VAS) will be used, and PONVs will also be recorded. After a 2-hour stay in the PACU, they will be transferred to the ward, and after 24 hours, they will be reassessed using the same parameters. Opioid consumption will be recorded in the PACU and during hospitalization, as well as the occurrence of nausea or vomiting and compared between the groups, and side effects and complications will be monitored.