I think it sounds more like a respiratory infection, could be pneumonia...did they not even do a chest x-ray to see if her lungs were congested. Heart failure sounds a lot like that to, she may need a diuretic. But she needs a vet to be sure. Lots of thoughts and prayers to you and I really hope she does improve, maybe some rest will help...
__________________ As Ever, Kathy 
Intruducing Bentley  Winston and Spencer: RIP My Sweet Angels |