Cardiopulmonary exercise test is a useful tool in the diagnosis and prognosis of patients with cardiovascular, pulmonary, neuromuscular and even metabolic disorders. The composition and the analysis of expired gas, and the characteristics of ventilatory dynamics, let us see how energy is transformed, within the cells (mitochondrial cristae), through several metabolic processes. Using the cardiopulmonary exercise testing, physicians can distinguish among several causes of dyspnea with undetermined origin. On the other hand, this test represents an important support to indicate the indication of a graft-transplant (heart, lung or both) in patients with severe heart disease, lung disease or both. Cardiopulmonary test has also been used to evaluate high performance athletes and patients with congenital heart disease. In the past, physicians and patients had a restricted access to the performance of a cardiopulmonary exercise testing, mainly due to the complexity and high costs of this technology. Nowadays, this kind of equipment has been simplified and the costs lowered, in consequence this test became a real alternative in daily work.