Hi friend,
Welcome to Health Care Magic
        There is an obvious spelling mistake - "3 years old"!!!???
      Feeling of ‘missing, dropping- skipping- hard- fluttering-’ beat is called ECTOPIC or premature beats / 
palpitation and so on is Dysrhythmia (
Arrhythmia is commonly used)...
      A beat comes earlier than normal – this itself is not usually felt. The next beat is a bit delayed - longer time to recover form early extra beat – so heart fills more and the beat appears forcible – thud / lubb - - dubb - - lubb - - dubb - lub - - - DUBB /
      Ectopic beats can arise from ventricle (lower chamber of the heart - Ventricular Ectopic; VPC) or Atrium (upper chamber - Atrial Ectopic; APC).  / APCs are generally harmless.  Even VPCs are often harmless – ‘benign’.   / If they are frequent - more than 5 per hour, 2 or more beats coming consecutively – they should be  investigated further.
      THE FIRST STEP IS TO SEE A CARDIOLOGIST / Irregular heart beats need to be DOCUMENTED by ElectroCardioGram (EKG).   / Standard ECG records the electrical activity of the heart, for a few seconds. It can detect the arrhythmia occurring during that time only.  If the episode occurs randomly or precipitated by a specific activity like exercise, one needs Holter or event monitor. 
     Anaemia / Anxiety / Alcohol / Tobacco (smoking) / Caffeine (too much tea, coffee, cola) / Fever / Infection / Pain / Stress / 
Thyroid / Vitamin D, calcium, 
magnesium / Medicines like 
Phenylephrine used for ‘cold’; 
Salbutamol used for asthma and so on - may be responsible.... / Illicit ‘drugs’ like 
Amphetamine are notorious to cause abnormal beats /  At times, abnormal nerve paths in the heart (bypass tracts) or disease of the conduction system may be responsible! 
See your doctor...
Take care
Wishing speedy recovery
God bless
Good luck