Welcome to HealthcareMagic.
if you have no other symptoms and no other abnormal findings on investigations , you do not need to worry.It could be completely normal for your body.
I advise you to visit your Cardiologist and get completely evaluated.if no underlying disease is found , try to practice yoga , meditation
to reduce stress or anxiety
and also to benefit your heart.
If you have very rapid heart beat at times you can try blowing pressure against closed glottis
for few seconds to reduce heart rate
If you need more information feel free to mail me.