I'm 44 and had open heart surgery five years ago, and had a stent put n my heart in 2010, is it safe for me to carry a baby?

Ask your heart Doc. This is not a question for the site. The best source of information about a complicated issue is the physicians who have examined you and know you best. I would schedule a visit with your heart doc and your prospective OB & seek their input.
Lifting. The sternum should be well healed after 3 months. You should be able to lift normally. If you mean to get pregnant, that is a serious decision with your OB gyn and cardiologist. You would have increased risk.