I haven't suffered from it and am not a doctor, but my uncle died from it so I'll tell you what I know.
The most common cause is long-term hypertension. As I understand it, the extent to which the damage to the heart muscle is reversible depends on its cause, so obviously there's no way anyone over the internet can give you any help with that, but if the heart muscle has hypertrophied I think non-surgical remedies are few.
As far as my uncle was concerned, he was encouraged to exercise - apparently it helps maintain such cardiac function as remains - and put on a low sodium, low fluids, no booze diet, as well as blood-pressure meds. He was never obese so that wasn't an issue.
That's all I can tell you, sorry.