Common causes of left-sided back pain include coronary heart disease, pneumonia, cervical spondylosis, etc. Go to the corresponding department in the hospital, and you may need to do electrocardiograms, blood tests, chest radiographs or CT tests. 1. Coronary heart disease: myocardial ischemia and myocardial infarction may cause pain in the precordial area or behind the sternum, radiating to the left side of the back, and at this time, electrocardiogram or cardiac enzymes can be done. 2. Pneumonia: Inflammation of the lungs causes inflammation of the pleura and chest wall, resulting in left-sided back pain, at this time to check the chest radiographs or CT and routine blood tests. 3. Cervical spondylosis: mainly neurogenic cervical spondylosis, cervical degeneration of the intervertebral disc oppression and irritation of neighboring tissues caused by the left back pain, at this time to check the cervical spine CT or MRI and so on. The left back pain may also have other causes, such as back fasciitis, muscle strain, etc. It is recommended to go to the hospital in time to improve the relevant examination, under the guidance of the doctor for standardized treatment.