Thanks for your comments and responses.

UPDATE: I took Chelsea to the vet specialist (cardiologist) for the ultrasound yesterday. They were impressed at how sweet and accomodating she was (despite trembling from being scared to death!).

The results is that there is some significant thickening of the heart wall. If untreated, and if it progresses, the 2 main problems are clotting which usually affects/paralyses the back legs and conjestive heart failure. And because cats typically don't show symptoms until they're really severe; there's no way of knowing how bad heart issues are until way too late.

We've caught it early and she's been presecribed daily medication to help keep the heart muscle from thickening further (I'm so looking forward to having to give her a pill every day for the rest of her life . . .)

To my surprise, after such a stressful day for her (that dreaded cat carrier/scary trip in the car/a stranger touching and looking at her - vet exam/getting her chest shaved/getting gooped for the ultrasound/getting ultrasounded/etc.) she was her sweet affectionate self when we got home (instead of Ms. Aloof-I'm-not-talking-to-you-because-of-all-the-horrible-things-you-did-to-me-and-I-don't-want-you-to-pet-me-or-pick-me-up-or-anything ---- I'm-just-going-to-sulk!).

So, despite my much lighter pocketbook, I'm hopeful that catching this problem early will keep it from getting worse.