risk for patients who have significant structural defects, and assessment of the physical capacity of postoperative patients The data obtained may be helpful in the decision process regarding therapeutic intervention, restriction of physical activity, and programs for rehabilitation or conditioning Evaluation of Rhythm Evaluation of the heart rate response and exercise-induced arrhythmias is essential in selected patients with surgically repaired congenital defects and in patients with known or suspected arrhythmias or inherited propensity to arrythmia Increasingly, exercise testing is used to assess the efficacy of pacemakers and to help guide programing parameters to improve exercise performance Evaluation of Myocardial Ischemia Screening for ischemia is a common reason for referral for exercise testing, particularly with left-sided obstructive lesions, such as aortic stenosis.33 In addition, a growing number of patients may be at risk for coronary arterial insufficiency after the arterial switch procedure.51 Evidence of abnormal myocardial perfusion as a result of Kawasaki disease is also not infrequent.45 Less common but, due to improved imaging, increasingly identified anomalies, such as anomalous origin of the coronary arteries and coronary arterial fistulas, place the child, especially the athlete, at risk for ischemia or arrhythmias.52,53 Evaluation of Exercise-Induced Symptoms of Uncertain Etiology One of the largest groups of patients seen in the exercise physiology laboratory is children who have various exercise-induced symptoms without an identified source Exercise testing may be useful in defining potential etiologies of symptoms Exercise-induced dyspnea, or new onset of exercise intolerance and fatigue, may be due to noncardiac causes, such as pulmonary, musculoskeletal, or hematologic disorders Evaluation of exercise-induced syncope or nearsyncope may result in the diagnosis of cardiac arrhythmias Evaluation of Exercise Capacity With Chronic Illness The treatment of certain noncardiac illnesses, such as childhood cancer, requires sometimes debilitating therapy The chronic effects of therapy, at times cardiotoxic as with Adriamycin, are highly variable It is increasingly apparent that many newer targeted cancer therapies can also have cardiotoxic effects.54 Evaluation of exercise capacity in these patients is valuable in identifying cardiovascular impairment, as well as for implementing rehabilitation therapy Data Obtained During Exercise Testing During each exercise test, obtaining as complete a set of data as possible is essential Occasionally, compromises are made regarding collectable data, especially in very young patients Nevertheless, it should be possible to obtain the following data Rate of Work The rate of work, or power, is measured in kiloponds per meter per minute (kpm/min) or, more commonly, in watts (W).55 The maximal rate can be measured directly on a cycle ergometer or inferred when a treadmill is used, based on height and weight, as well as treadmill speed and grade For this reason, when using a treadmill, it is often more instructive to use the exercise time for analysis rather than the estimated rate of work, comparing the time to normal values based on age, height, weight, and gender Normal values for maximal work rate in healthy children are approximately 3.5 W/kg in postadolescent boys, and 3.0 W/kg in preadolescent boys and girls regardless of age.37 In the absence of other measurements, maximal work rate provides only limited information The rate of work is reassuring if it falls within the normal range However, low values do not give any information as to the cause of the limited rate Therefore, measurements of aerobic capacity, maximal and at the ventilatory anaerobic threshold, are usually more useful in the evaluation of exercise performance Aerobic Capacity These values are generally presented as maximal consumption of oxygen, and the consumption of oxygen at the onset of the ventilatory anaerobic threshold Large variations in these measures are secondary to body size Because of this, the values are generally normalized for body weight: milliliters of oxygen consumed per minute (mL/min) per kilogram of body weight Maximal consumption of oxygen in children varies depending on the type of protocol and ergometer used and, to less extent, on the age range of the subjects.41,56–58 As stated previously, values obtained on a treadmill are approximately 10% higher than with a cycle ergometer Normal values for