A tread mill test will evaluate the perfusion of oxygenated blood of the heart vessels when the demand increases due to heavier than normal workload of the heart, and then there will be an evaluation on the time to recover at rest. The test will determine (usually if there are any vessel blockage) or interference to normal blood flow...underlying cause can be due to plaque buildup, malformed vessels, heart structure, etc.
It would be helpful to know health history, any other tests, on medication, etc.
Hope this helps, and if you have any further questions you are welcome to respond. Thanks for sharing. Take care.