Good question.
I am 40 and have been lifting for quite a while. I have been on for a couple of years now.
I had a stress test done a year or so ago (the real probelm was heartburn, not anything with my heart), and the doc and the tech both noticed that the WALLS of the heart were thickened. This is common among serious lifters. And it should go away after you stop.
In terms of enlarging the heart, I am not sure if it would or why it would. Lifting makes my muscles thicker, not larger.
Your doc probably won't know anything about this.