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I understand your concern. Apart from a fast heart rate, ECG (electrocardiogram) is normal. Causes of a fast heart rate can be anxiety, fever, dehydration, anemia, and thyroid disorder, especially if the heart rate remains that high even at relaxed and calm times. Chest pain is unlikely to be cardiac because cardiac chest pain does not occur like this, especially in young people with no family history of premature coronary artery disease, no diabetes, no hypertension, and no other risk factors. Chest pain can be due to chest infection, muscular strain, gastric reflux, or costochondritis (inflammation of rib joints). I hope you find it helpful. Kind regards.