Air-bronchograms are noted. There is a bulge in the area of the left atrium and left auricle . There is more evidence of peribronchial disease . As this is a large breed dog the most likely diagnosis is dilated cardiomyopathy. Dilated cardiomyopathy occurs in large breed dogs at mid age, usually not this old.
Older dogs are more likely to have heart failure due to mitral valve insufficiency.
Cardiac ultrasound revealed evidence of both mitral valve insufficiency and dilated cardiomyopathy as causal for the heart failure.