Summary: This report describes an ultrasound-guided medial and lateral pectoralis nerve block using liposome bupivacaine, performed before the surgical incision, in a patient undergoing submuscular breast augmentation. The anatomic basis and technique are described. This procedure may be offered to patients undergoing submuscular insertion of a breast implant or tissue expander. Advancements in ultrasound guidance allow for more precise anatomic placement of local anesthetic agents. The injection technique used for this procedure resulted in complete relaxation of the pectoralis major, facilitating the surgical dissection and markedly diminishing postsurgical pain and muscle spasms.