The pain in the upper part of the left arm may need to consider physiological causes and pathologic causes, the latter such as tendonitis, acute injuries, cervical spondylosis, colds and so on. 1. Physiological causes: if you are engaged in the work of heavy hand-carrying for a long time, it may cause pain in the upper part of the left arm, in this case, it is recommended to take reasonable rest and relax and massage the muscles in time after work, and the symptoms will disappear gradually. 2. Tendonitis: this is a kind of sterile inflammation, which can cause pain in the upper part of the left arm. 3. Acute injury: for example, muscle strain or suffer external blows, muscle damage, can also lead to pain, in addition, there may also be swelling, limited activity and other symptoms. 4. Cervical spondylosis: When cervical spondylosis compresses the nerve roots, the above symptoms may also occur, and may be accompanied by numbness, neck pain and other symptoms. 5. Viral colds: when you have a cold, you may also experience pain in the upper part of your left arm, in addition to fever, fatigue, sneezing, runny nose and other symptoms. There may be other reasons for the pain in the upper part of the left arm, when there is pain in the upper part of the left arm, it is recommended to consult a doctor.