What is the likely cause?
These features suggest mitral regurgitation. The main differential is of mitral stenosis. Presence of significant left ventricular enlargement is a feature of mitral regurgitation (volume overload) but is not seen in mitral stenosis.
The rough outline of the left atrium (yellow) can be inferred by the presence of a double border on the right (green arrow), splaying of the carina (blue) and prominence of the left atrial appendage (red arrow).