In mitral stenosis "the double shadow" on X ray chest PA view is due to enlargement of -

Ans. is 'c' i.e., Left atrial enlargement * In Xray chest PA view as the left atrium enlarges in mitral disease, it first fills in the left cardiac waistline, so that the left cardiac border becomes convex instead of concave.* Then the left atrium extends to the right so that its margin is visible along the right heart border, above the profile of right atrium and overlapping it - referred to as the double shadow.* Thus the double shadow is a classic sign of left atrial enlargement.