Borderline cardiomegaly is a slight degree of heart enlargement can be seen in obese patients, especially when there is concomitant high blood pressure. The more important concern is whether the heart pumping function is abnormal - this is more of a determinant in whether you have a cardiomyopathy (pathological enlargement).
"Superior mediastinal widening related to of great vessels..." mediastinal is widing of space and a partition separating adjacent parts within the chest cavity and "superior" is the space above the pericardium (above the heart). Left ventricular enlargement relates to the heart's left chamber (pumping chamber). Thoracic aorta is the section of the aorta located in the chest area. There can be a congenital deformity, form tortuosity causing obstructive or non obstructive coarctation (closing, blocking).