I Have 2 Stints One In July 2009 And 2nd

I have 2 stints one in july 2009 and 2nd in aug,2015 After month of second stint, when I walk for 5-10 min. or talk on phone for 10-15min or lying on bed I feel shortness of breath and little chest tightness.
I have 3rd angiogram two days before and cardiologist told that I have nothing wrong with my heart condition.
Is it may be due to any lungs condition or something else.