Cardiomegaly involves two main processes in the heart muscle. Hypertrophy causes the heart to enlarge due to thickening to the cardiac muscle, and dilation causes enlargement due to stretching of the heart muscle. Dilation occurs as a result of volume overload in the heart.

The left ventricle can be enlarged from two broad underlying conditions: dilation and hypertrophy.

Left ventricular dilation can occurs as a result of volume overload. Conditions that cause volume overload can be further broken down as follows:

• Valvular Disease: More common underlying valvular heart disease conditions would include mitral regurgitation and aortic regurgitation.
• Congenital Heart Disease: Patent ductus arteriosus and a ventricular septal defect.
• High output states resulting in volume overload: Anemia and thyrotoxicosis.
• High stroke volume states: Complete heart block and prolonged severe sinus bradycardia.
• Can occur as a result of ischemia and remodeling.

Left ventricular hypertrophy occur due to factors that can cause the heart to work harder than normal. Cardiac hypertrophy is seen in the following condtions:

• Hypertension
• Aortic valve stenosis
• Hypertrophic cardiomyopathy
• Atheletic training

Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology