Heart Failure (HF) and Atrial Fibrillation (AF) are two conditions that commonly occur together. Clinical guidelines consider a resting heart rate of 100-110 beats per minute (bpm) acceptable for patients with HF and AF while 72 bpm is considered the average in healthy populations. A higher resting heart rate indicates that the heart is working harder to meet bodily demands, and though it may be considered safe for patients with HF and AF to have a heart rate of 110 bpm, the investigators believe it is having a significant negative impact on patient quality of life and their ability to exercise. The current study will test exercise ability using a treadmill test before and after either a cardioversion, where the patient's heartbeat is reset using electric shocks, or a pace and ablate method, where the patient receives a pacemaker to regulate their heart rhythm and an ablation (intentional damaging) of the node that coordinates the beats within the heart. This will allow investigators to compare how the heart responds to exercise when the patient is on rate-control and anticoagulation medication therapy (before cardioversion or pace and ablate) and after the procedures. During exercise, the investigators will do a blood test that lets investigators know how efficiently the heart is working and record any symptoms experienced. The investigators will also collect information about the patient's quality of life. Using this information, the investigators hope to better understand whether the current standard of a resting heart rate of 100-110 bpm is ideal for patient quality of life.

Inclusion Criteria:

1. Age ≥ 18
2. Persistent or Permanent Atrial Fibrillation
3. HF - NYHA class II-IVA despite guideline-direct medical therapy
4. Rate controlled
5. Able to perform stress test
6. Scheduled for clinical P&A OR cardioversion

Exclusion Criteria:

1. Creatinine >180 μmol/L or eGFR <30 mL/min/1.73 m2
2. Significant valvular heart disease: Moderate to severe tricuspid regurgitation, mitral regurgitation, mitral stenosis, aortic regurgitation, aortic stenosis
3. Patients who have had a TAVI, valvular surgery, or CABG within 3 months of enrolment
4. Right ventricular systolic pressure >50mmHg
5. Existing pacemaker
6. In sinus rhythm
7. Predictable vasovagal syncope to pain and sight of blood

Patients who have been clinically scheduled for either a P&A or a cardioversion procedure.