Mitral regurgitation is a frequent finding in patients with aortic stenosis scheduled for aortic valve replacement. Detection of mitral regurgitation in such patients has important implications, as it can independently affect functional status and prognosis. When mitral regurgitation is moderate to severe, a decision to operate on both valves should only be made following a careful clinical and echocardiographic assessment. Indeed, double-valve surgery increases perioperative and postoperative risks, and mitral regurgitation may improve spontaneously after isolated aortic valve replacement. Better understanding of the determinants of these changes appears particularly crucial in the light of recent advances in percutaneous aortic valve replacement.