It's called tachycardia and can be caused by some external stimuli like caffeine, some over the counter meds or emotional stress or anxiety. It can also be cause by a cross circuit in your heart's electrical system. You need to see a doctor if your heart rate routinely goes over 100 bpm.
Jon
hi erijon, thanks for your reply, I am not on medication & donot drink alcohol, let me explain what happen lasted evening, around 6:00pm I felt my heart fluttering hard on my chest for a few seconds, I had 7 episodes from 6:00pm until 7:30pm same evening, I had another one today, I also experience this 2 weeks ago I had 5 episodes in 1 hour. 2 years ago i was ill for 7 weeks..... my symptoms were tiredness, severe headaches, upset stomach,dizziness to the point of getting blackouts I went to the doctor & was tolded my blood pressure was 153/110, my bp been 110/75 for some months now.I am female 32yrs weights 115 height 5'3 .