My Father had stent in the heart done in 2012, will it cause any issue for the medical examination ?
It depends. for PGP, the medical need to pass not only for contagious disease (would applies to spousal sponsorship) but they cannot have condition that would need excessive medical demand. And that applies to PGP applicants, and their dependents. (as well as new PR applications under other economic streams)I don't think so. It is not a contagious disease that could put Canadian public at risk. and I hope your father lives a long healthy life.
But if the procedure was done so many years ago and he is in good condition, then there shouldn't be anything to worry about. At the end, there is nothing you can really do now. Do not try to hide that from the medical exam because they can find out. And if so, it would be misrepresentation for not disclosing it.
Regulatory Definitions Related to Excessive Demand - Canada.ca