Yes, heart failure will cause the abdomen to fill with fluid. I am so sorry.
I lost a bird to heart failure last year. I could hear her heart valves clicking a few months before her heart gave out. (you can put your ear over their back where the neck meets. The lungs are beneath this area, heart beneath the lungs.)
I am an lvn and when I saw her I thought to myself she is presenting like a patient with congested heart failure. I will get more chicvs this spring and I will not go back to the local breeder. Vet said sometimes the people breed the chicks without knowing how to mix breeds and the ChicKS have heart problems peritonitis egg binding more frequently etc
But I want buff orpingtons I have four salon faverolles and I thin adding a few more orpingtons would make a nice flock