Hi
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Sharp chest pains that come and go can be due to angina or due to costochondritis. In the latter you will be able to find a tender spot on the chest. Otherwise with your medical history, chances of angina are more. Please inform your cardiologist regarding this and do not take up any strenuous activity.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
I would guess the sharp pains may be ischemic (lack of oxygen to areas of your heart in this case) in nature, due to your two blockages. Not to say it couldn't be something else, but with what you've said, that's what I would guess (I'm not a doctor).