Hi My Brother ( Age 53 )had Mild Heart Attack

Hi
my brother ( Age 53 )had mild heart attack yesterday while on duty.
he was admitted to hospital and treatment given by docs.
as per cardiograms and diagnosis docs said it was mild attack and paitents health is ok and can be discharged tomorrow.

Now, docs has suggested for angiography.

I want to know if the health condition of paitent is stable then why angiography is needed.