<s>[INST] my 17y/o son has brief episodes of tachycardia about once a week. these episodes last about 20 seconds and only cause palpitations, no other symptoms. these episodes never occur with exercise. He is a cross country runner and never has palpitations when he runs. He does not consume caffeine or other stimulants. He has never had dizziness, chest pain, SOB OR OTHER SYMPTOMS. His resting heart rate is around 50. RECENT NORMAL LABWORK INCLUDING THYROID, CBC, ELECTROLYTES AND EKG.  ALSO, HE HAD NORMAL 24 HOUR HOLTER. SHOULD I BE CONCERNED? [/INST] Hello and thank you for using Chat Doctor. I carefully read your question and I understand your concern. I will try to explain you something and give you my opinion. You should not worry about. This thinks are quite normal in Jung ages. Fast heart rate might be related to emotion, physical activity and different pathologies like anemia, hyperthyroidism, electrolyte imbalances, cardiovascular disease. As you explain, you already have done all the examinations, and they result normal. This is a very good think. So, this fast heart rate might be just sporadic, related to emotions. The only thing that I would suggest is a cardiac echo to complete all the examination, but in my opinion you should not be concern. We meat in our daily practice sucChatDoctorplains in Jung ages. Hope I was helpful. Bestregards, Chat Doctor.  </s>