Pain in the left upper arm is commonly caused by cardiac-related referred pain, frozen shoulder, radiculopathy, and traumatic factors. 1. Heart disease-induced referred pain: commonly caused by acute myocardial infarction or angina pectoris referred pain, patients often appear left shoulder pain. 2. Frozen shoulder: this is one of the most common causes of pain in the upper arm and around the shoulder, mostly manifested as pain in the shoulder joint and unfavorable movement. 3. Neurogenic cervical spondylosis: most of these diseases are related to nerve root compression, and most of them manifest as numbness and radiating pain in the upper limbs. 4. Traumatic factors: upper extremity fractures, soft tissue injuries, rotator cuff injuries, etc. caused by direct or indirect violence can also trigger pain. For the frequent occurrence of left upper extremity pain, it is necessary to consult the hospital in time and complete the relevant examinations, and follow the doctor’s instructions for treatment after a clear diagnosis.