<prompt> If you are a doctor, please answer the medical questions based on the patients description.My 15 year old son has occasional fast heart beat with no physical activity. He has ADHD and takes Adderrall 20 mg.1 time a day. He s 5 5 weighs approx. 110 lbs. I took him to a pediatrics cardiologist who listened to his heart took an EKG. All normal but he prescribed him to wear a heart monitor for 1 month, but of course my teenage son thinks it s a nuisance won t wear it now. This morning he comes into my room while he s getting ready for school and has me feel his chest. His heart was beating fast, almost like pulsating. He said he felt fine had no shortness of breath. It went away within a minute or two. What can be causing this? I m worried yet he seems okay with it and doesn t want me to tell the doctor. I think he should have an ultrasound.  <response>: Hello, I would agree with you on the fact that a cardiac ultrasound would give more information on his heart structure and function and exclude possible congenital heart defects. I would also recommend checking his thyroid hormone levels for thyroid gland dysfunction and his blood electrolytes for possible imbalance. A complete blood count should be checked too, in order to exclude possible anemia, which can trigger ectopic heartbeats. Hope I have answered your query. Let me know if I can assist you further. 