Your stress test results can be either positive or negative.
If your stress test result is negative
In most cases, a negative stress test means that there is no underlying heart problem present, or at least nothing serious (see Figure 1). However, for this negative result to be meaningful, it is important that the person exercises strongly, to the point where the heart rate and blood pressure rise.
For example, if a young person doesn't exercise forcefully, and quits the test early, the negative result may be due to the fact that that heart wasn't exercised enough to uncover the presence of a narrowing or blockage of an artery.
So, particularly in the case where the cause of chest pain is being evaluated, a negative stress test result is most reassuring following a good exercise performance.
A negative result can also occur in a person with known heart disease, for example, following an old or even recent heart attack. Even if one artery is blocked, the others may be good, and sometimes even new channels form to bring blood and oxygen to previously diseased areas of the heart.
These new channels are sometimes called "nature's bypass." In these situations, the person undergoing the stress test will have a negative result, with no symptoms or abnormalities on the ECG. This is a good result. These patients do not usually require further evaluation with an angiogram.
In other situations, such as following a surgical procedure or after completing a healthy heart program, a negative result on the stress test provides objective proof to both the patient and doctor that the procedure or program has been beneficial.
If your stress test result is positive
A stress test result is considered positive when there is a specific change on the ECG (see Figure 2). In most cases, these ECG abnormalities occur because of an inadequate blood supply due to a narrowing or blockage in one or more of the coronary arteries. In many people with "silent" heart disease, these ECG changes can occur without any symptoms being felt.
If your stress test result is falsely positive
A stress test can also show a falsely positive result. This means that the test incorrectly shows a positive result when it should be negative. This occurs more often in women than men, possibly due to hormones that cause ECG changes.
The test can also be unreliable in patients with certain valve diseases such as mitral valve prolapse.
When there is uncertainty regarding the reliability of the stress test result, a similar test can be done using nuclear or radioactive material to increase the accuracy of the test. This is called a MIBI or thallium test.