My cat Morag, who is a Burmese, was diagnosed with severe HCM by my regular
vet about a month ago, after having undergone an ultrasound.  Yesterday she
saw a cardiologist at the veterinary hospital here, and after an ultrasound
was performed using a machine with a higher resolution than the one
previously used, the cardiologist said that she has a very unusual heart
condition that doesn't fit into any textbook.  She actually only has mild
HCM, but the problem is that her heart is abnormal.  Her left atrium is
huge, and her left ventrical is just abnormal.  The wall bulges inward in
several places and also the ventricle contains crap, stuff that strings from
one side of the chamber to the other.

She doesn't have HCM, DCM, or RCM.  The cardio said that what she has is
rare, nobody knows what causes it, how to treat it, or what the prognosis
is.  All that can be done is to treat the symptoms, so try to keep the lungs
clear and try to prevent her from throwing a clot.  There are some theories
of how the heart became this way - some say it's due to inflammation, some
say scar tissue from a previous viral infection, some think it's auto-immune
in nature, and some think it's congenital.  The jury is still out.

The cardio says that she has seen perhaps a handful of cats in her career
with a presentation similar to Morag - the most interesting point she made
was that out of that handful of cats, the cat with the heart that most
closely resembles Morag's was also a Burmese.  So I'm wondering if anyone
has heard of this before in Burmese cats (or in any cat).