[Rose n Poos]

When was the last time a chest x-ray was done? This is my memory talking but for my Noel, our vet at the time, took views in which even I could see that her trachea was being impinged on, and her heart had enlarged from the previous xray.

 

[Rose n Poos]

Heart Failure in Dogs: 6 Practical Tips From Veterinary Cardiologists

Heart failure in dogs is a complex condition, but successful management is possible. Here are practical tips for managing heart failure.

todaysveterinarypractice.com

This link has an xray which shows what the compression may look like.
It's stated that the dog is not necessarily in heart failure for the compression to be a problem.