Pain under the left shoulder blade is usually a referred
pain from abdomen like
stomach ulcers, pancreatitis, or from the
chest like in heart attack, pericarditis, pleuritis, pneumonia, pulmonary embolus, lung cancer and aortic dissection. It could also be a pain due to acidity and acid reflux. If heart issues have been seriously looked into then lung, pancreas and acidity related issues should be ruled out. Since the pain is referred to arm too pericarditis should be ruled out.