In this histological study, the canine infraspinatus tendons were repaired to different bone surfaces: 1, a tendon end adjacent to the insertion: 2, a calcified fibro-cartilage layer; 3, a cancellous surface. Tendon repair to tendon ends restored the four-layered enthesis in the healing period, whereas tendon repair to the calcified fibrocartilage considerably delayed fiber development into bone. Fiber connection to cancellous surface developed according to the remodeling of trabecular bone by 12 to 16 postoperative weeks. Therefore, ruptured tendons should be attached to the remaining end or to a cancellous surface; they should not be attached to a calcified fibrocartilage layer.