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Your mother is diabetic and now that she is TMT positive this means that she has coronary artery
disease, although she may not have angina pain or other symptoms.
I am sure she must be taking treatment for it as in diabetic reduction in blood supply to heart may occur without sympotoms what is known as silent Ischemia
Please visit a Cardiologist and after proper assesment this can be decided that a Angiograpgy and revacularization procedure is required or not.
If risk is low even a CT Angiography
may be planned if this is normal she can continue on medicines and if significant lesions are detected she will require a Caheter Angiography and plasty if required.
Her other risk factors should also be taken care like Lipid Profile
,Blood sugar level,and High BP