Left back shoulder pain can have the following causes: First, heart disease, when the heart has a heart attack, angina pectoris, can appear radioactive pain on the back of the left shoulder, often accompanied by pain and discomfort in the anterior thoracic region, it is necessary to check the body early, early examination of the heart electrocardiogram, ultrasound and imaging to early diagnosis and treatment. Second, shingles. In the early stage of shingles, there can be pain on one side of the back of the shoulder, and after the incubation period, there can be clusters of herpes, which should be diagnosed and treated early at the dermatology department. Third, lung disease, when there is a tumor or inflammation in the lung, there can be pain in the back of the shoulder, then it is necessary to check the lung CT for early diagnosis and treatment. Fourth, scapula and rib diseases, when there is a tumor in the scapula and ribs, there can be pain in the back of the shoulder at the ribs and scapula, so it is necessary to check the CT and ECT of the ribs and scapula for early diagnosis and treatment.