I also started having high heart rate and even developed a murmur that my primary and other doctors dismissed at normal variation in a lot of people and nothing to worry about but then when it started to causing skipped beats and I couldn’t keep up breathing wise and would be exhausted they sent me to a cardiologist and again echo, ekg, stress tests and even holter was fine and nothing was addressed. I went to mayo for brain lesions, fatigue and muscles they heard the murmur and wanted to do echo and found Bicuspid Aortic valve which is a congenital heart defect. I’m not sure about other congenital valve disorders but this one does cause high heart rate (resting above 100bpm) so sometimes it seems maybe they don’t have capabilities with medical imaging in other hospitals or maybe not specifically knowing what to look for as well? I found out after that my grandpa and great grandpa died of heart disease and my aunt also has same issue. Still makes me wonder if he was ever told specifics or was having valve monitored for prevention of heart failure. So 100% any doubt deserves second opinions. I have two echos one normal and one not within months and scary.