It is not uncommon at all to feel discomforts after open heart surgery. Your body has been through a very traumatic event. After my bypass, I watched the weeks go by, but feeling no improvement. You start to convince yourself that things will never improve. After three months, I started to notice a small improvement each day.
If you mean the chest wall underneath the left breast, it might or might not be normal. It just depends on what is going on. If you mean the breast itself, I really don't know what to make of that, except that you should see a doctor. I assume you've already complained to your surgeon, cardiologist, PCP, and/or OB-GYN? May I ask what he, she or they said? This could be so many different things.