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.
It would also be important to know if the wall of the left ventricle is too thick or too thin.