I have a constant pain (feels like pulled muscle) under my xiphoid process. I noticed it last night when going to bed - particularly when lying on my left side. I am 60 yr. Old. No history of heart disease. I was out shoveling heavy/wet snow for an hour e

Chest pain. While it may be only musculoskeletal, given your age and the circumstances that led to the pain, the wisest course of action is to immediately go to the er for cardiac evaluation. No adult male with chest pain should assume it is not heart related until they have been properly evaluated. Go now without further delay.
This . This is almost certainly related to a muscle strain. Particularly if you didn't have any symptoms when you were shoveling snow earlier, it's very unlikely to be related to your heart. That it bothers you more when you are quiet and in a particular position also argues that the discomfort is musculoskeletal. An anti-inflammatory pain medication should help - aspirin, ibuprofen, naproxen, Acetaminophen - depending on what medication you tolerate most easily and works best for you.