The cardiopulmonary exercise test is a valuable method for quantifying global cardiovascular function. It is quantitative, cheap, safe and highly reproducible. Unfortunately, it is highly under-utilized in favor of less quantitative, more expensive and perhaps less safe and reproducible methods. But even if performed, the peak Vo2 is often the only measurement made, and the data for determining the patient's anaerobic threshold (AT) and other parameters are discarded by the examiner. The discarding of such valuable physiological data is likely due to the lack of recognition by the physician that these measurements, and the physiological parameters that could be calculated from them, reflect cardiovascular function. Furthermore, the information can be extracted without additional expense. The AT, as a marker of the severity of cardiovascular function, is particularly, under-utilized relative to its clinical usefulness. With the development of the V-slope method, the AT is easily measured in all patients whose exercise is limited by cardiovascular factors. While the AT is a very valuable measurement in all patients, it is especially valuable in patients who should not be maximally stressed, e.g., the elderly or post-myocardial infarction patients.