Cardiopulmonary exercise test for diagnostic and prognostic purposesThe functional assessment of patients with dyspnea usually uses static or submaximal exercise tests, which provide limited information because they do not expose patients to the real situation that causes exercise intolerance. The cardiopulmonary exercise test (CPET) is an increasingly used tool that can be used in these circumstances. It determines peak oxygen consumption, anaerobic threshold and cardiac and respiratory reserves, measuring oxygen uptake and carbon dioxide production during standardized exercise conditions. It is useful for risk assessment in cardiothoracic surgery and can provide valuable information such as the timing for transplant in patients with severe chronic disease. The test is non-invasive, has a short duration, and exhibits an adequate safety profile in specialized centers. It is mainly indicated for the dynamic evaluation of athletes or patients with heart, respiratory, and neuromuscular diseases, it is essential part of the study of dyspnea of unknown origin, and in the prognostic assessment of patients who face highly complex interventions. This review provides a comprehensive review of CPET with emphasis on its main indications in healthy people, athletes and, in particular, in functional evaluation of patients with exercise limitations in the context of their chronic diseases.