For the question of what causes left back pain, there are many clinical causes, the most common of which are the following: 1, if the patient has angina pectoris or myocardial infarction, it will be implicated in causing pain in the left back. 2, if the patient has a tumor or infection in the left lung, it will also cause pain in the left back. 3, the most common is local muscle strain, local muscle sprain, local myofasciitis, which will cause pain in the left back, Local muscle sprains and local myofasciitis can cause painful symptoms in the left back. For such patients, it is usually possible to apply hot compresses and topical ointments to activate blood stasis and slowly get better.4. Cervical spondylosis, when compressing the nerve roots of the spinal cord, will also cause pain symptoms in the left back. For such patients, it is necessary to actively conduct a cervical spine CT or MRI examination to clarify the diagnosis and then treat the symptoms.