We will recruit patients who are referred for clinically indicated pacemaker implantation

Inclusion Criteria:

1. Adults aged over 18 with left ventricular ejection fraction >35% and one or more of the following guideline based ventricular pacing indications:

1. Permanent or intermittent 3rd degree AV block
2. Permanent or intermittent Mobitz type II AV block
3. First Degree AV block with a pacing indication
4. Slow chronic Atrial Fibrillation or Proposed AV node ablation
5. Bifascicular block with a pacing indication
6. Trifascicular block with a pacing indication
7. Wenckebach with a pacing indication

Exclusion Criteria:

1. Patients who are likely to only need occasional ventricular pacing, i.e. those with isolated sick sinus syndrome.
2. Pregnant women.
3. Unable to provide informed consent.
4. Those with comorbidity leading to a life expectancy <1year.