The common causes of the left chest muscle always jumping are spasm, calcium deficiency, subcutaneous neuritis and so on. 1. Spasm: If there is impact on the left chest, strenuous activities, etc., it may cause chest muscle jumping, which can be relieved after resting under normal circumstances. 2. Calcium deficiency: If calcium deficiency causes hypocalcemia, muscle twitching, dry and dull skin and other symptoms may occur. 3. Subcutaneous neuritis: Subcutaneous neuritis can be manifested as tingling, tenderness or burning pain, which may also be accompanied by muscle throbbing, soreness and itchy feeling. The left chest muscle always jumping may also be caused by other reasons, if you can not relieve or severe pain should go to the hospital in time to find out the cause and targeted treatment.