Hello there, Is there any fever which is causing a fast heart beat or tachycardia ? Please check temperature and ensure there is no fever. There are other causes of a fast heart beat and not everything can be attributed to some underlying heart problem. Thyroid problems in children can result in a fast heart beat. But usually such conditions will have other associated behavioral changes. Fever with a low white blood counts can signify a viral infection in your child. You have mentioned that not all the problems occur at once. So the complains are rather vague. It is unlikely that your child has a heart problem as ECHO and ECG are normal with no cardiac findings on examination. Lastly do assess his behaviour at school. Many children avoid going to school if they are facing some problems and try their best in fabricating an illness. But lets not take chances. Do keep everything in mind. At the moment there is nothing to worry. Take care.