If your cardiologist has evaluated you and feels as though the functions of your heart and valves are satisfactory, then from a plastic surgical perspective I can see no reason why a breast augmentation can't be performed safely. You will want to have the input of the cardiologist first before undergoing anesthesia or surgery to make sure that you can be expected to tolerate it safely.
This is best decided by your Cardiologist who knows you and your heart very well. It depends on the severity and your ability to withstand the anaesthetic and the operation.