It would also be important to know if the wall of the left ventricle is too thick or too thin.
I assume you have a fact based question, such as the results of an echocardiogram, and analysis by the technician and cardiologist.
An enlarged heart can be congenital, result of high blood pressure (but I think that would take more than 30 years), and it could simply be a result of extreme exercise... the last point is a guess-from-memory that has the least credibility - but I offer it in case the subject is a marathon runner or similar. "Regular" exercise would not cause such, I believe.
What did the doctor say, was there any concern, or just a statement of the fact? Enlarged left atrial can cause atrial fibrillation, not sure what symptoms, if any, would go along with an enlarged ventricle.