Take a deep breath
Really. Chest discomfort is not usually cardiac.
If taking a deep breath makes it worse, if it occurs spontaneously, if touching the area reproduces the discomfort, if it lasts a long time, if not associated with activity or other associated symptoms, if you are younger with no risk factors or family history, you can probably relax. But, your mileage may vary, so if any doubt, see your doctor!