Does my dog have Heart Disease or Heart Failure?

[tammy m]

My 8 yr old black lab, Nala has been swollen for over a month in and out of the vet. They give her diuretic and it goes down then comes right back finally went to see a specialist. She did an x-ray and drained fluid in her chest cavity but told me her heart looked good. All labs are good but she sent the fluid from her chest out and now tells me it's indicating something is wrong with her heart. And we are going for an ultrasound on Friday. I'm so scared - How long can a dog live on Meds for heart failure?
40 minutes ago - 1 week left to answer.
Additional Details
3 minutes ago

When the specialist did the x-ray she also did just a quick ultrasound for me to look at her heart and look around for any tumors. She didn't find any tumors and she said she didn't measure her heart but that it looked good that she didn't see any signs of heart failure but said but I didn't measure anything.