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If you had been cleared 25 times, then there is n heart disease
It is Anxiety
Neurosis / when centred round the heart, it is called Cardiac Neurosis
Get a planned appointment, instead of emergency, every time.
Have HOLTER (24 to 48 hour ambulatory monitoring) / ECHOcardiogram
/ TMT (Treadmill exercise ECG) / LABORATORY work-up - not to confirm but to exclude and convince
Have Psychiatric assessment and assistance.
Don't worry. You are very young and will have a great future.
Wishing speedy recovery