Ask your dad's oncologist about having a MUGA scan done at the radiology (nuclear medicine) lab.
The scan will establish a baseline for the efficiency of your dad's heart function. One of the negative side effects of Sutent is it can possibly cause damage to your heart. I just recently had my 3rd MUGA Scan having been on Sutent for over a year now. My oncologist said he had another patient that had suffered damage to his heart from the Sutent. FYI my scan came back clear.
Good luck and Happy New Year!!!