Fever 2 1/2 weeks after hole in heart repaired

My 3 year old grandson had a procedure (not open heart surgery) that repaired the hole in his heart by a miniature umbrella inserted through his groin.  Now 2 1/2 weeks later he has had croup and a fever.  He was seen by his regular pediatrician who did not give antibiotics.  His croup disappeared and the high fever went away.  Now--five days later a low grade fever has returned.  He still has general virus symptoms (congested nose and phlegmy cough).  I have told my daughter to call the cardiologist.  Should my grandson be on antibiotics given the recency of the surgical procedure?

concerned grandmother

[Cleveland Clinic]

Probably not.  These vital infections usually don't cause bacterial problems.  If the fevers persist however, he should have an echo of the heart to rule out any evidnece of infection there.