What is the likely diagnosis for a patient presenting with redundancy of the mitral valve leaflets and a midsystolic click heard best at the apex?

The presentation of redundancy of the mitral valve leaflets along with a midsystolic click best heard at the apex is characteristic of mitral valve prolapse (MVP). In MVP, there is an abnormal elongation of the chordae tendineae or excess tissue within the mitral valve leaflets, which leads to the valve leaflets bulging back into the left atrium during ventricular contraction. This anatomical change is responsible for the midsystolic click, which occurs due to the sudden tension on the chordae tendineae as the leaflets prolapse.

This diagnosis is often associated with a benign course, but it can sometimes lead to mitral regurgitation if the valve fails to close properly. Understanding the specific heart sounds associated with MVP, including the click and any potential murmur of regurgitation, is key to distinguishing it from other conditions that affect the mitral valve.

In contrast, the other conditions mentioned do not typically present with the combination of symptoms observed in this case. Aortic stenosis is characterized by a different type of systolic ejection murmur and does not involve mitral valve prolapse. Mitral regurgitation presents with a holosystolic murmur rather than a midsystolic click.