Hi, it sounds like he is describing 'ectopic' beats. Caffeine will make these worse. They are not harmful but they don't feel very nice at the time. (I speak from 9years of experience). If you google ectopic beats you will get an in depth explanation of what they are. I hope this may help. Good luck.
For a good explanation, please read this great article posted at medhelp by pacperson: http://www.drjohnm.org/2013/06/benign-pvcs-a-heart-rhythm-doctors-approach/