What would an echo stress test show....that a regular echo test doesn't?

Change w/exercise : When excercised, or 'stressed', the heart needs more oxegen to function properly than at rest. If it's not getting that increase, the muscle will start to move in abnormal ways, which will show up on the echo. At rest, because it needs less oxegen, it may be getting enough, so it will look normal then.

Wall motion....: Stress echo will show stress-induced wall motion abnormalities immediately after stress. Often stress-induced wall motion abnormalities are not seen in other types of imaging such as myocardial perfusion spect since the heart images are not taken immediately after stress. Occasionally post-stress stunning may be seen on myocardial perfusion spect.