I believe the nuclear stress test are said to have up to a 10% margin of error.
If you are concerned, ask your cardiologist about doing a 64 slice CT of the Coronaries or a Cardiac Cath. Those procedures could provide more definitive answers than a
stress test -- in light of continuing symptoms, it would be worth it to put your mind to
rest.
The accuracy of the test depends which test and the local expertise in the test. In ladies with large breasts a dobutamine echo is a very good test and reduces the imaging artifacts.