Pain in the middle of the left rib cage, consider the following causes: 1. coronary heart disease, unstable angina pectoris, acute myocardial infarction. Patients may present with dull pain in the anterior or left side of the chest, with crushing pain that may radiate to the back, which may be accompanied by palpitations, dizziness and weakness. doing electrocardiography, cardiac enzyme troponin test may help in the diagnosis. 2, myocardial pericarditis, patients with myocardial pericarditis may present with left-sided chest pain. 3, intercostal neuralgia, intercostal neuralgia often presents as throbbing pain in the corresponding area, lasting for several seconds.