Dear friend, welcome and thanks for entrusting your query here at HCM!
I am Dr. Prasad Akole (Critical Care Expert- http://bit.ly/Dr-Prasad-Akole) and am glad to address to your query here.
The results of nuclear cardiac perfusion scan showing a defect most probably means that there is poor perfusion (blood supply) to an area of the heart.
In the background of his past heart attacks, it does mean that this area is not getting blood supply due to a blocked coronary artery
(supplying that part).
You should be guided by your cardiologist and continue treatment for him as advised.
I hope you are fully satisfied with the guidance I gave.
I would be glad to answer any further queries. Please ask for any clarifications before closing and rating this answer.
Thank you and Good luck!