Hello MG,
The fluttering sensation in your chest is probably Premature Atrial or Ventricular Contractions (PACs and PVCs). These are quite normal and common with or without heart disease, and can be provoked or aggravated by caffeine, nicotine, anxiety, stress, sleep deprivation, inhalation of noxious fumes, etc. The list is quite long, and sometimes there is no apparent reason for them.
To be on the safe side and to decrease your worries about the flutters you may want to seek out the opinion of a cardiologist.
This is just my opinion and remember I am not a professional.
Be well,
Kitt