Welcome to HCM,
Your father Father is had CABG in 2009 and one valve replaced, He may be taking treatment regularly it is just by chance he started shortness of breath
during his visit.
The most likely cause appears he is developing heart failure
which precipitated by AF( Atrial Fibrillation
) There are no details about his 2 D Echocardiography
how much is his LVEF..
Please have faith in Cardiologist we treat patients and not investigations, CT and MRI are useful test if used judiciously and getting them without indication is not required.Please continue treatment and go for investigations if advised by your Cardiologist.
Please take care of him