A coughing sheepdog…
This middle aged pup presents to you with a history of coughing and exercise intolerance. What do you think?
There are a couple of important things to note on these radiographs. First is the very large cardiac silhouette. Note that you will see references to the cardiac silhouette in a radiology report, rather than 'heart', because technically you can not see the heart on a radiograph (unless the pericardium has been removed surgically). Because of this, you can't truly call the heart enlarged, you can only call the cardiac silhouette enlarged. Thus, when considering differentials for this case, be sure to include both primary cardiac disease (cardiomyopathy, chronic valvular disease) as well as pericardial effusion.
The second pertinent finding in this case is the generalized interstitial pulmonary pattern which is worst in the hilar region of the lungs. This distribution of pulmonary infiltrates is most compatible with pulmonary edema secondary to left-sided congestive heart failure.
So your radiographic diagnosis for this case would be pulmonary edema due to left-sided congestive heart failure. Cardiomyopathy is the most likely underlying cause given the size and shape of the cardiac silhouette, but an echocardiogram is indicated for further evaluation.