Ischemia meas that your heart does not get enough oxygen under certain circumstances.
If this only happens during vigorous exercising, it is obviously not a real problem.
If ischemia happens with only very light physical activity, it might be a problem. Not only for the surgery but also for the physiotherapy sessions afterwards.
If the ischemia is found very recently, your might ask your doctor about the extend of the ischemia and the impact of if on your upcoming surgery and rehabilitation.