It is premature vascular contractions. I've been setup with heart monitors and they tell me I'm ok. It feels like my heart pauses and restarts. I usually don't notice it until I'm resting/quite. The doctor said that it comes from not enough sleep and caffeine.
I've also had super tachacardia. Where my heart was beating about 170 beats a minute. The doctor said that came from too much thyroid medicine and caffeine. I've since weaned myself off thyroid medicine.