Hi friend,
Welcome to Health Care Magic

A normal EKG and enzyme levels are reassuring and exclude a heart attack!
Normal X-ray is helpful to rule out enlargement, failure and lung pathology
A murmur that has once present and disappeared later is well known and may be ‘functional’ or a little hole at birth that could have closed subsequently.
A ‘little low Hb’ is most likely from bleeding.
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The changes could well be from anxiety, added on by the hormones. However, it is advisable to have it investigated.
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Anxiety / Alcohol / Tobacco (smoking, chewing) / Caffeine (too much coffee, cola) are common causes.
Medicines may be responsible – like phenlephrine used for ‘cold’ / salbutamol used for asthma / Illicit ‘drugs’ like amphetamine are notorious to cause abnormal beats
Occasionally, there are abnormal nerve paths (bypass tracts) in the heart.
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     If a routine ECG does not show, 24 to 48 hour ambulatory monitoring (Holter) is done to analyse and plan for further management
ECHOcardiogram is necessary to see the heart valves (Mitral Valve Prolapse) / heart muscle (Cardiomyopathy) and heart function (Ejection fraction, wall motion abnormality).
Treadmill exercise ECG (TMT) is done to exclude Ischemia (reduced blood flow) –though it is not likely in view of your young age.
     Did the laboratory work-up include electrolytes (potassium in particular), thyroid (over-active)?

If there are no clues and if you are still bothered by it to the extent of interfering with life style, there are more tests. The treating doctor may suggest them depending on need, based on his assessment of the situation. They are advanced techniques of investigations of increasing complexity (and invasive) – like Electro Physiological Studies (EPS) > it resembles angio / a catheter is put inside the heart, electrical activity recorded, stimulation and suppression tests are carried out, suitable medicine tested and so on. Though the test is the gold standard, it is invasive and has a minimal risk and is not generally done unless there are compelling indications. This super-speciality expert is called ELECTRO-PHYSIOLOGIST.
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     Specific treatment is not always necessary.      The first line medicine is generally beta blockers, like Metoprolol – slow release and small dose. It will benefit both anxiety and missed beats. Your doctor will give proper prescription and follow up
     If they are not effective and if the problem is severe, several other classes of drugs are available – acting by different mechanisms - the specialist will decide tailored to your needs / they may have side effects and need follow up.
There are other advanced treatment modalities - like RF ablation, which could be done during EPS.
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FOLLOW UP WITH YOUR CARDIOLOGIST
Relax. You are young; you sound intelligent – you stand an excellent chance of returning to normalcy.
Be positive – why fear the heart beats faster? The problem is only if it could not beat! You are tolerating the rate well - means that you may not have any basic disease of the valve, muscle and so on.
Be in touch with your doctor - it is a question of time and you will be well.
Medicine is well advanced nowadays – management is possible for almost all situations...

Take care
Wishing speedy recovery
God bless
Good luck

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