Tramadol is a pain killer that is made from the alkaloids in opium, poppy seeds. It can be a significant drug but the dosage is always important. Percocet contains acetaminphen and oxycodone, another powerful pain killer.
You should certainly consult your doctor about mixing these two drugs, the dosage as well as your physical stature including age and weight are significant in determining any potential health risks.
If we look at the potential affects on the heart there are not too many. Assuming your heart is healthy in the first place you shouldn’t have a problem mixing these two drugs in small dosages. Acetaminophen will thin the blood, that is not really a problem; however there is no way of positively identifying the risks to one specific person without a medical history and a current health assessment, the safe assumption is that it is bad to mix any drugs without a doctors approval.
Check out this link for more information on Tramadol
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a695011.html