Atheromatous is plaque buildup. The aorta can include the aorta valve (one-way-pass of blood from left ventricle to body), the root of the valve and the aorta vessel. If there is plaque buildup in any part of the aorta that will cause higher resistence for the heart to pump against.
Cardiomegaly of the left ventricle indicates an enlargement of the pumping chamber (left ventricle). The enlargement is due to the abnormal burden the heart is pumping against with the atheromstous.
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Ken