Ventricular enlargement usually displaces the lower heart border to the left and posteriorly. This is true whether it is right ventricle (RV) or left ventricle (LV), as the RV, when enlarged, tends to push the LV to the left and back. The best way to tell RV from LV enlargement is to look at their outflow tracts. If the pulmonary arteries are enlarged and the aorta is diminutive, the RV is probably enlarged. If the aorta (ascending, knob, or overall) looks enlarged, it is probably the LV. Remember, both may be enlarged at the same time!
Left atrial enlargement makes a convexity between the left pulmonary artery and LV on the frontal view and may make a round double density‚ just inferior to the carina and seen through the right atrial contour on the frontal view. It also displaces the descending left lower lobe bronchus backward on the lateral view. Right atrial enlargement (rare as an isolated finding in adults) causes the lower right heart border to bulge rightward.