heart size varies greatly. The measurements are a guide to other tests, diagnostic criteria. Having a chamber which is bigger or smaller than the average norms setup doesn't mean a thing if everything else checks out. People come on this board A LOT worried because they read on their report that something was bigger or smaller than usual, but then eveything else checks out so it's not a big deal.
I recall seeing a study that a very high load of PVCs can cause some muscle changes (>15,000+ PVCs / day) which they found to reverse itself when the PVC burden was reduced.
Visit this link about PVCs, it's written by an Electophysiologist, a heart rhythm specialist.
He mentions 20,000 PVCs per day, over weeks or months, before cardiomyopia, or weakening of the heart muscle, would occur. It seems like too many PVCs reduces the strength of the heart muscle, so it doesn't seem like it would cause enlargement of the heart.
The size of a person's heart varies by genetic factors, weight, height, blood pressure, also conditioning, and likely other factors, so there can be significant variations in size person to person.