Welcome to HCM,
Your father having chest pain
, and his angioplasty
with DES ( Drug Eluting Stent) it must be investigated to rule out angina
,kindly get your 12 lead EKG to see changes in cardiogram.
I hope you must be taking other drugs like anti platelet agents and statin
In the mean time he can use sub lingual nitrates.
If there is nothing serious then proper medicines may be advised for his pain . He may have pain due to non cardiac causes also.
I hope his stent is not blocked but you must contact your cardiologist and examined and investigated properly to know the cause so that corrective measures may be taken.
In worst case we may have to plan for CABG( Coronary Artery
Please take care.