The enlargement may be due to the exercise and not pathogenic. Or it could be the normal size for you!
An EKG is not a reliable source to determine chamber dimensions...ekg is useful to to determine rhythmetic problems. An echocardiogram can give an estimate of dimensions that has some validity, if there is any concern. I doubt you have a heart problem if you can walk at a good pace for 1 1/2 miles there are no symptoms with exertion. If you have a patthogenically enlarged heart, there usually is a fast heart rate at rest (over 100) and shortness of breath with exercise.
I would certainly agree with KenKeith. The EKG can show a problem with wall thickness, but usually checks the electrical system of the heart. You said nothing of seeing a cardiologist. You said your primary doctor did this EKG. If you have a serious heart problem, you wouldn't be able to walk like you discribe. If you are concerned, see a cardiologist for further testing.
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