Objective measuring techniques have been explored, but were unsuccessful in dogs because of the extreme variation in breed conformation. Cardiac measurement techniques were more successful in the cat as the body type is fairly uniform. However, subjective assessment of cardiomegaly by the experienced viewer was found to be equally effective in the diagnosis of cardiac changes, and is the most practical method of assessing disease on thoracic radiographs. This occurs commonly in obese animals where fat is deposited within the pericardium. Athletic dogs may have slightly larger hearts normally.
Puppies appear to have larger hearts relative to their body size.
This apparent cardiomegaly usually disappears by about 6 months of age. Breed conformation causes a tremendous variation in cardiac size and shape. Radiographs cannot differentiate between dilation and hypertrophy. Because of the many factors causing artifactual heart enlargement, mild or even moderate cardiomegaly should be considered minimally significant unless supported by changes in clinical signs, ECG, or echo findings. Usually seen in conjunction with LV enlargement Lateral view dorsocaudal border enlarges, becoming somewhat triangular in shape, extending into the caudal lung fields dorsal deviation of stem bronchi, primarily the left.