A defibilator is very good to maintain a stable reliable heartbeat. The cardiomyopathy can be the underlying cause due to an enlarged heart.
The enlarged heart (dilated) can be successfully treated and return to normal size. About 6 years ago, I had an enlarged heart, and the heart was very weak and blood backed up into the lungs causing congested heart failure. Currently with medication, exercise, proper diet, etc. my heart has returned to normal and functions adequately. I wasn't expected to live more than a few months...I was ICU for several days to get a normal oxygen level and remove excessive fluids.
I read a statistic that 1/3 viral cardio's are cured, 1/3 live with their condition, and 1/3 don't survive. Your son is young and is being treated so that is an advantage for a favorable outcome....take into account the particular diagnosis/disease your son has, the stage treatment began, your son's age, current state of health, and quality of medical care available. Different people will have different outcomes--but an aggressive, well-designed can be effective.
I am providing a link to thread that may give you perspective. Sorry for your son's medical health! Hope this helps.
http://wiki.answers.com/Q/If_you've_been_diagnosed_with_viral_cardiomyopathy_is_it_a_guaranteed_death_sentence