Spitting with blood inside, left side of the sternum pain may be circulatory diseases, respiratory diseases, trauma and other reasons related. 1. Circulatory diseases: such as mitral stenosis, can cause pulmonary stasis caused by alveolar wall or bronchial endothelial capillary rupture, can appear chest pain, hemoptysis symptoms. 2. Respiratory diseases: such as tuberculosis, tuberculosis lesions involving the pleura can be manifested in the early stage of chest pain, when the necrotic part of the tuberculosis involves the wall of the pulmonary capillaries, there can be the phenomenon of spitting with blood inside. 3. Trauma: If the left side of the chest is hit and other external injuries, it can cause local tissue damage, which may cause chest pain and spitting with blood. It is recommended that people with blood in spit and left-sided sternal pain go to the hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of the doctor, so as not to delay the condition.