Congenital mitral regurgitation, as an isolated pathology, is very ususual but does occur. Initially the pansystolic murmur can be thought to be a ventricular septal defect. If you get to see the plain film before an echo is done, you can nip in with the diagnosis. The left atrium is bigger in mitral regurgitation than it is in VSD. Beware the lung fields as mild plethora can look very similar to mild upper lobe diversion.