It means it's sad that doctors don't explain things to us.
A human heart should be the same size as the persons "closed fist".
I think if he didn't say anything else to you, that he must think your OK.
But if your still concerned, you can always see a heart doctor (a cardiologist) for more tests. A cardiologist is more experienced with the heart and will be able to tell you if all is well. If your heart passes all the tests, then the size make no difference.
Having an over sized heart is much more dangerous.
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