I suspect you will be on the same tablets my husband is on, he has dialated left sided cardiomyopathy, it was diagnosed by a echocardiogram, wonder if you had on of those while you were in hospital.
Getting fit and watching your weight generally are important as we have found out.
My husband takes his weight every morning when he first gets up, and writes it in a diary, as we were told to do by heart rehab unit which we attended as asked to by the hospital we attended.
When his weight has gone up suddenly I take him to the hospital and show them our record in our diary, that makes them sit up and take notice, and admit him to find out what is going on.
Get your GP to send you MRI results to your cardiologist as it might have some importance, especially as it now tells you something that contradicts what he told you.
I keep an old computer case that has copies of all my hospital appts letters, ECG results in envelopes, letters the hospital has written to my GP, letters the specialists incl private specialists have written to my GP, MRI results and even x-ray results. blood test results. I have found this very useful when we present at the hospital, and the young Dr then says ''oh this is an old file'', well this isn't old, its up to date current what would you like as I lift up my bag they assume is just a laptop I am carrying, after five years it is starting to get heavy.
I have educated myself on my husbands condition, from zero to start with, borrowed books from the library, researched online, not forums, looked for university papers, dr to dr papers and have now got a very good understanding of cardiomopathy or so I am told by Dr's who treat him and they will talk not as a patient but maybe as a nurse.
One Dr told me he would employ me on the cardio wards anytime, he said my instincts are very good, I have saved my husbands life 4 times now by taking him to the hospital in time when I have suspected something is wrong.
Don't second guess yourself, get your local Dr on your side, use him to help educate yourself, take his advice and ask questions, husbands last urgent heart episode was missed by even specialist's but i kept argugiing with them and saying it is not right, I proved to be right in the end, very usual pain in his left arm and putting on weight NOT NORMAL, end result is he had deveolped complication of his electical system closing down very slowly in his heart, and finally failing, a pacemaker and defib later, an I have my energizer bunny back