I agree with Flycaster, shortness of breath can be very serious. When I went to emergency care, it was the only symptom required so stated by the nurse. I thought it was a respiratory problem, but it turned out to be congested heart failure...I was shocked!!!
Shortness of breath should always be checked out. It is entirely possible it could be that his stented areas are blocking again or new blockages are forming. I'd suggest he go his health profressional asap.