The causes of pain in the upper left back include muscle strain, coronary heart disease, lung disease, myocardial infarction, cervical spondylosis, ankylosing spondylitis and other causes. 1. Muscle strain: It is caused by the strain of shoulder and back muscles due to frequent sedentary or a posture for too long, and aseptic inflammation occurs, which is accompanied by stiffness and limited activities in addition to pain. 2. Coronary heart disease: the pain can radiate to the left upper back, accompanied by panic, chest tightness, chest pain, lasting less than 30 minutes, which can be clarified by electrocardiogram. 3. Lung diseases: such as pneumonia, pleurisy, lung cancer, usually accompanied by cough, sputum, hemoptysis and other symptoms, which can be clearly diagnosed by chest CT. 4. Myocardial infarction: coronary artery vascular occlusion with obvious chest pain radiating to the left side of the back, lasting more than 30 minutes. 5. Cervical spondylosis: cervical spondylosis can involve the left back pain by compressing the nerves, and radiate pain and numbness to the upper limbs. 6. Ankylosing spondylitis: Hyperplasia and ankylosis of the spine can cause back stiffness, pain and limited movement. There are many reasons for the pain in the upper left back, if it persists without relief, you need to go to the hospital in time to see a clear cause of the disease, targeted treatment.