Yesterday i started to have a sharp, pulsing pain under my left pectoral muscle. i have had it all day today.?

Doctor can evaluate: A primary care doctor or a doctor in the E.R. Can evaluate to see if there is a problem with the pectoralis muscle, the ribs/cartilage of the chest, the heart and it's large vessels such as the aorta, the lungs, the esophagus, etc... A chest x-ray can be done to look at the heart and lungs. Further testing is available, if needed.