suspected of having, cardiac anomalies However, abnormalities of noncardiovascular origin may also play a role in limiting exercise performance even in patients with surgically repaired complex congenital cardiac defects Any malfunctioning of the muscles, bones, blood, or nervous system will impair exercise performance Therefore a modern laboratory for exercise physiology must be capable of assessing all exercise-related systems, including the cardiovascular, pulmonary, neurologic, hematologic, and musculoskeletal systems Furthermore, accurate interpretation of exercise tests requires the proper equipment and personnel This is particularly important as the cardiologist supervising the laboratory frequently evaluates children with real or suspected exercise limitations These children seldom have any cardiovascular abnormalities but may have involvement of other organs, such as dysfunction of the pulmonary or musculoskeletal systems Properly performed exercise testing and its interpretation should also be able to identify or exclude abnormalities of extracardiac organs that normally contribute to exercise performance This chapter briefly reviews basic exercise physiology as it relates to cardiopulmonary exercise testing Discussed are the equipment required for performing an exercise test and its applications as well as assessment of the types of data obtained from exercise testing and their usefulness in the evaluation of the child with cardiovascular disease Also reviewed are indications and contraindications for exercise testing in cardiovascular disease Basic Exercise Physiology Assuring proper exercise performance requires the seamless and continuous meshing of multiple systems of organs.3,4 The classic illustration of Wasserman and colleagues (Fig 23.1) depicts the interaction of the key systems that couple internal cellular respiration to external pulmonary respiration during exercise It shows the systems as a series of overlapping cogs, all of which must mesh seamlessly to allow exercise to occur In such fashion, mechanical energy is produced from chemical energy at the cellular level, with subsequent delivery and removal of substrates for energy production and byproducts of muscle metabolism All of this is accomplished while maintaining chemical and thermal homeostasis within narrow ranges FIG 23.1 Functional interdependence of the multiple organ systems during exercise The meshing gears represent the musculoskeletal and the cardiopulmonary systems, which interact to ensure adequate delivery of oxygen to, and removal of byproducts from, the exercising muscles The smooth continuous interactions of these multiple physiologic systems are essential for proper function of the muscles during exercise (From Wasserman K, Hansen JE, Sue DY, et al Exercise testing and interpretation: an overview In: Principles of Exercise Testing and Interpretation, vol 1 2nd ed Philadelphia: Lea & Febiger; 1994:1–8.) Cellular Metabolism Adenosine triphosphate is the chief source of chemical energy for the exercising muscle Mechanical energy is produced by the process of excitation-contraction coupling, driven by the breakdown of adenosine triphosphate and the release of inorganic phosphates and adenosine nucleotides The stores of adenosine triphosphate and phosphocreatine in the myocytes are sufficient only for 10 to 15 seconds of activity and so must continuously be replenished As can be seen in Fig 23.2, adenosine triphosphate is produced in small amounts in the cytosol by anaerobic metabolism Much larger amounts are produced aerobically in the mitochondria.3,5