Pain and swelling involving one foot only can be due to many reasons;
It can be due to Arhtritis (joint inflammation), especially if there is painful movements of ankle joint or infection of the joint; There are some kinds of arthritis (like Gout) which can be flared up whenever there is stress on the body like a cardiac problem or any procedure being done on body.
It can be due to cellulitis (infection of the skin) if there is no pain on movement of ankle.
Another possibility is of poor circulation due to clot formation (especially if the affected foot is cold and bluish).
At this point, sine you just had a cardiac stenting done, I will suggest you to go to ER for a comprehensive clinical examination discussing the possibilities I have mentioned, as some of the reasons for this pain and swelling may need urgent intervention.
You can take Tylenol for pain relief for the time being --- but do not delay an examination.
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