Yes, HCM can be secondary and controlling the thyroid can reverse the HCM,
or at least make it much better. Thyroid problems are treatable and the HCM is
in that case. However, cats can have Hyper T AND heart disease as separate
conditions, so its good she has treatment.
If the first treatment doesn't work, there is another older drug in a
different class. Not sure what its name is though.. (It's not an -azole..) You need
to get the thyroid under control if you can. Then see whether that brings
the heart condition under control.
An ultrsound is the only way to see the heart's damage.
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