EXercise Cardiac Magnetic Resonance Assessment of Left Atrial Mechanics Following Ablation

This study is examining how the heart's left upper chamber (the left atrium) recovers after a procedure called catheter ablation for atrial fibrillation (AF), which is an irregular heartbeat. Researchers will use MRI scans of the heart — both at rest and during exercise — to look at how the heart mechanics improve after ablation. **You may be eligible if...** - You are 18 or older - You have been diagnosed with paroxysmal AF (intermittent irregular heartbeat that comes and goes) - Your heart's pumping strength is normal (ejection fraction at least 50%) - You are scheduled to have catheter ablation for your AF - You are able to speak, read, and understand English **You may NOT be eligible if...** - You have persistent or permanent AF (not the intermittent type) - You have had a previous ablation procedure for AF - You have a pacemaker or defibrillator implanted - You have significant kidney disease (eGFR below 30) - You are pregnant - You have certain other heart conditions such as hypertrophic cardiomyopathy, cardiac amyloidosis, or pulmonary hypertension - You have had prior heart surgery - You are unable to complete an MRI or exercise test Talk to your doctor to see if this trial is right for you.