Heterotopic ossification (HO) within the substance of the subscapularis tendon is a rare lesion which remains a poorly described condition with little known of the exact mechanisms involved. Furthermore, its clinical importance remains still unclear. To our knowledge, there are no studies present to data regarding HO within the substance of the subscapularis tendon, even with resultant isolated complete tear of the subscapularis tendon. Here we present a case of huge HO associated with unusual isolated complete tear of subscapularis tendon concomitant with tear of biceps long head tendon. After arthroscopic debridement for the complete tear site of biceps long head tendon, mini-open excision of the ossification and subscapularis repair with suture anchor fixation were performed. The patient showed complete recovery of strength and function of the subscapularis at subsequent 24 months follow up.