I was diagnosed with cardiomyopathy in 2002 and was in the very severe category. The likely cause was very high blood pressure. Medication brought that down and the DCM returned to normal, until last spring.
Although the blood pressure was normal, when the DCM returned I had developed an irregular heart beat. I ended up having an ICD fitted, some of my earlier BP meds being reduced and I also got two new drugs, digoxin and spironolatone, to control heart rate and fluid retention. The lung congestion has gone and I can sleep much better now and the fluid retention has disappeared. I walk 20 mins per day and cycle on a trainer 2 x 15 mins per day. Nothing mad, but I have a pulse monitor with an alarm set at 110. I don't want that ICD to have to revive me so I stay within cautious limits. I am more concerned with keeping things moving than striving to get fit.
Although losing weight won't cure the weakened heart muscle, which has become overstretched and is not as elastic as it used to be, it does mean that the heart is not required to do as much work as when you are carrying too much weight. So, it's worth doing, if you can avoid the exercise killing you
Don't overdo it, as they say.
It's a question of taking things slowly and being patient. Don't rush, don't panic, avoid stress, do everything in your own time. Just think of doing nice things in the future and look forward to enjoying a new life. I won't be looking forward to mountain biking in the alps, which had been my wish, but I can still look forward to cycling the continental river routes, following the river flow in the downhill direction. It's not cheating. You don't have to make things hard as some people seem to think.
Oh, and avoid salt! But I guess they've drummed that into you already.