Common causes of bulging left neck tendons include injury, jugular vein varicose, and occupying lesions. 1. Injury: Injury to muscles, ligaments or fascia may cause localized spasms, leading to bulging of the neck, or damaged adhesions of the right side neck muscles, causing bulging of the left side of the neck. 2. Jugular venous distension: chronic pulmonary heart disease, restrictive cardiomyopathy, pericardial effusion, tension pneumothorax and other diseases can cause jugular venous distension, which may cause the left side of the neck bulge. 3. Occupational lesions: neck tumors, fibrous tumors, lipomas and other occupational lesions may also cause the left side of the neck bulge. The bulging of the left side of the neck may also be caused by other reasons, and you should go to the hospital in time to find out the cause and carry out targeted treatment.