The risk is not high but it is does happen. Patients should be questioned for a history of fainting with exercise, known cardiac abnormalities, and a family history of sudden cardiac death at a young age. If there is a yes answer to any of these inquiries or if the physician hears a click or murmur with a stethoscope, an EKG should be obtained and/or the patient referred to a specialist before stimulants like Ritalin are prescribed. It is safer to take natural supplements and look for food allergies to treat ADHD. It is not a standard guideline, but the same questions might be asked during a pre-participation PE for sports, with a similar workup if any of the answers are positive.
See the from the American Academy of Child and Adolescent Psychiatry, Dr. James J McGough of UCLA presenting.