I am so sorry you are so frightened and disappointed that your surgery was put off or pushed back is maybe a better way of stating that.
My sister is in the hospital with ovarian cancer and renal failure. She needs surgery but they will not do it until she is cleared by cardiology so know you are not alone. This is standard operating procedure.
I am sure you will be fine but it is best to make sure then go ahead blind into surgery..............know I am thinking of you.