When sleeping on my leftside i get a slight ache on my leftside of my chest and move to the other side?

Chest discomfort: If this is the only time you experience chest discomfort it doesn't appear to be a serious problem. Lying on your left side may pinch an intercostal nerve or muscle that runs between 2 ribs. Some people complain of feeling their heart beat while lying on their left side. If you still have concerns, see your MD for evaluation and advice.