Children with known heart defects, or patients with suspected heart defects typically are  the primary recipients of stress tests. There are numerous reasons why this may be done, including the evaluation of heart rhythms, ischemia (whether the heart muscle is receiving enough oxygen), or if the patient can produce symptoms during exercise, the extent of exercise capacity, and aerobic capacity at peak exercise.
It is often important to evaluate children who have had a cardiac surgery in order to compare these patients with those who are normal. Patients with minimal cardiac defects often have exercise tolerance that is comparable to their peers, but those patients with significant cardiac defects will seldom compare to their normal piers.
Aerobic capacity in patients with compromised hearts is an important determinant when evaluating these children for possible surgical intervention. For instance, patients with a tetralogy of fallot or significant pulmonary regurgitation or other pulmonary problems will exhibit significant pulmonary distress during exercise.
Measuring blood pressure during exercise is also important. Normally, systolic blood pressure should increase during exercise, and diastolic blood pressure should decrease. Abnormal blood pressure responses during exercise may indicate a significant cardiac defect. If systolic blood pressure is blunted or decreases during exercise, this may indicate such defects as a significant left ventricular outflow obstruction, pulmonary hypertension or anomalies of the coronary arteries. (See my posts on these subjects).
Echocardiography
This non-invasive test should be routinely done on any child suspected of a congenital heart defect. As an echocardiographer, it has been my experience that many pubescents who die as a result of strenuous exercise often have at least one of two primary defects: IHSS, or idiopathic hypertrophic sub-aortic stenosis (a deformation of the outflow tract of the left ventricle), or anomalous coronary arteries (a defect in the arteries that feed the heart muscle).
Most congenital heart defects should be found with this procedure alone, and is typically done on many infants and adolescents.Stress echocardiography is also an important tool in the evaluation of myocardial ischemia. This test involves exercising the patient in conjunction with standard echocardiography. Nuclear perfusion imaging is another exercise related test that evaluates myocardial perfusion. this test involves the injection of a radioisotope via and intravenous connection, and an X ray device that can evaluate the oxygen content of the heart.
Conclusion
In the end, exercise testing may aid the pediatric cardiologist in their effort to evaluate whether surgical intervention may be required, or in the cases of those who have had repairs, how well these patients are responding to their surgery. Furthermore, it is important to evaluate whether arrhythmias or ischemia develop during exercise. Additionally, physicians wish to know how high blood pressures become with peak exercise, and whether there is any exercise induced asthma.