The Vagus nerve is responsible for some aspects of the heart's rhythm, slowing it at appropriate times, and also involved with digestion. The nerve courses along the esophagus, onto the stomach, and further. I had a situation where, by the end of a day, every time I swallowed food, my heart would skip a beat. My wife thought I was nuts, I invited her to take my pulse, and I proved it would skip with every swallow. She worked for my cardiologist and discussed it with him, he said it was probably a Vagal response. /en.m.wikipedia.org/wiki/Vagus_nerve
Things are more complex with our bodies than most people realize. There is a process called Respiratory Sinus Arrhythmia, more pronounced in younger people, where the heart rate increases in rate as we breathe in, and slows as we breathe out. I felt this effect on my dog years ago, he was sleeping and I rested my hand on his chest. I could feel his heart rate, but it was constantly changing. I noticed the changes coincided with his breathing in a predictable way.
Many subtle changes occur in rate to changes in blood pressure, as you are sitting and stand, move around, get scared, it's constantly tweaked. It's a miracle we don't notice more skipped beats. If you've been tested and are determined not to have an underlying problem, PVCs are very common and not a concern.
This link casually mentions magnesium, I thought it may interest you. www.drjohnm.org/2013/06/benign-pvcs-a-heart-rhythm-doctors-approach/