1. As with all surgeries there is risk of heavy bleeding, still as your MD's has ruled out Warfarin
as the cause of bleeding, make sure there isn't any internal source of bleeding like blood clot!
2. use of NSAID's (non-steroidal anti inflammatory drugs) medicine after CABG can cause bleeding and blisters and history says he is taking ASA
), so it can be a cause of the symptoms mentioned above!
3. talk with your MD regarding the possibility so that necessary adjustment can be made in time.