Left atrial enlargement can be seen on
a dorsoventral view as a bulge at the 2-3 o'clock position, and on the lateral view
there is separation of the mainstem bronchi with the left bronchus being forced dorsally.
Left ventricular enlargement is recognised on a lateral view by straightening of the caudal
border of the heart, sometimes becoming convex, and loss of the caudal cardiac 'waist'.
The trachea is elevated dorsally and the presence of pulmonary venous congestion
is recognised by enlargement of pulmonary veins, and the presence of pulmonary oedema
(interstitial and/or alveolar), particularly in the perihilar region of the lung
Right atrial enlargement is recognised on the lateral view by cranial bulging of
the cardiac silhouette, and on the dorsoventral view by bulging at the 10 o'clock
position. The trachea is elevated over the cranial part of the heart on the lateral
On a lateral view right ventricular enlargement causes increased sternal contact
and increased convexity of the cranial border of the cardiac silThe apex of the heart
is sometimes lifted off the sternum. The trachea is elevated over the cranial heart.
Right-sided heart failure results in passive venous congestion of abclominal structures
and radiographic evidence of hepatomegaly, spleand ascites are often present as well
as enlargement of the caudal vena cava. If there is underperfusion of the lung, pulmonary
arteries and veins may appear thin and the lung parenchyma radiolucent.
A large rounded cardiac silhouette is indicative of pericardial effusion (though
in younger animals peritoneopericardial diaphragmatic hernias or per cardial cysts
may give a similar radiographic appearance). Positive contrast studies using an image
intensifier may be useful to demonstrate valvular regurgitation during systole.