Upper arm pain on the left arm may be caused by physiological reasons such as overstrain and cold, or it may be caused by cervical spine, myocardial ischemia, myofasciitis and other pathological factors. 1. Physiological reasons: the left upper arm has biceps brachii, triceps brachii and many tendons, ligaments and other soft tissue structures exist, if it is the left side of the habitual hand of the people, long-term lifting heavy objects or the left side of the upper arm for a long time of the activities, there may be fatigue damage to the soft tissues of the left side of the upper arm, causing pain. In addition, the left upper arm for a long time by the cold, will cause local small blood vessel spasm, may also appear the above symptoms. 2. Pathological factors: when cervical spine has degenerative lesions leading to cervical spondylosis, due to displacement of cervical intervertebral discs, the left spinal nerve root or spinal nerves are compressed, and there are sensory and muscular abnormalities in the innervated area, which may also be manifested in the symptoms of pain in the left upper arm. Coronary artery stenosis may cause ischemia of the heart muscle, and radiating pain in the left upper arm, left shoulder, and left back may also occur. Chronic strain or other causes of aseptic inflammation of the muscles or fascia of the left upper arm, which irritates the surrounding tissues, may also lead to pain. The symptoms of pain in the upper arm of the left arm alone can sometimes not accurately determine the cause, but also need to be combined with the characteristics of the medical history, other test results in order to make an accurate judgment, it is recommended to clarify the cause of the disease under the guidance of a doctor, and standardized treatment.