The PRIMARY Ancillary Substudy is looking at two ways to fix a heart valve problem called mitral valve regurgitation (MR). This happens when the mitral valve doesn't close properly, letting blood flow backward in the heart. The study compares two treatments: MVr (Mitral Valve Repair) and TEER (Transcatheter Edge-to-Edge Repair). Researchers want to see how these treatments affect the heart's structure and function over time. They will look for changes in heart tissue and check for heart rhythm problems, which can lead to serious issues like heart failure or sudden death. The study will involve up to 250 patients across several countries and will last about 12-18 months. CMR (Cardiac Magnetic Resonance Imaging) and TTE (Transthoracic Echocardiogram) are imaging tests used to study the heart before and after treatment. Some patients will also have small pieces of heart tissue, called biopsies, checked during surgery.

• The study lasts about 12-18 months with follow-ups 12 months after starting.
• Participants might need imaging tests and possibly a biopsy.
• Patients must be part of the main PRIMARY trial to join this substudy.