We have developed and are using an algorithm for the interpretation of cardiopulmonary exercise tests that are performed in our Pulmonary Diagnostic Service Department. As its decision points, this algorithm uses routinely obtained measurements from the results of these exercise tests, such as VO2, VCO2, VE, SaO2, HR, and AT. Using the algorithm results in an objective determination of limitation to exercise and allows for the differentiation between pulmonary and cardiac or circulatory limitation. This straightforward technique for arriving at an interpretation of these tests has resulted in a more consistent approach to interpretation and an excellent teaching guide for physicians and technicians.