Clinical expertise
Dr Iain Sim is a consultant cardiologist and electrophysiologist specialising in all heart rhythm disorders, with a specialist focus on arrhythmia and cardiac devices.
He regularly treats patients with conditions such as:
- atrial fibrillation
- coronary artery disease
- heart failure
- heart palpitations
- supraventricular tachycardia (SVT)
- syncope (fainting)
- Wolff Parkinson White syndrome
- ventricular tachycardia
He performs treatments such as:
- ablation of atrial fibrillation
- ablation of SVT
- ablation of ventricular ectopics
- implantation of pacemakers, defibrillators and cardiac resynchronisation therapy
Locations
Our specialist provides care at these locations:
Biography
Dr Iain Sim is a consultant cardiologist who specialises in the diagnosis and treatment of heart rhythm disorders (arrhythmias) at Harefield Hospital. He manages a full range of cardiac conditions including chest pain, breathlessness, palpitations, fainting (syncope), coronary artery disease and heart failure.
His clinical expertise spans catheter ablation for atrial fibrillation (including pulsed field ablation), atrial flutter, supraventricular tachycardia (SVT), ectopic beats and ventricular tachycardia, alongside complex cardiac device implantation including pacemakers, defibrillators (ICDs) and conduction system pacing. His further interests include inherited cardiac conditions and in identifying and protecting patients at risk of dangerous heart rhythms.
Dr Iain Sim qualified in medicine (MBBS) from St George’s, University of London and is a Member of the Royal College of Physicians (MRCP UK). He completed a PhD at King’s College London and holds a Certificate of Completion of Training (CCT) in Cardiology, with specialist accreditation in electrophysiology and cardiac devices. He undertook advanced specialist training at leading UK cardiac centres including Royal Brompton and Harefield Hospitals, King’s College Hospital and the Royal Sussex County Hospital, where he developed extensive expertise in heart rhythm disorders, electrophysiology procedures, and implantable cardiac devices.
Research
Dr Sim completed his PhD within the cardiac electrophysiology and imaging group at King’s College London, under Professor Mark O’Neill. His work focused on the mechanisms that drive atrial fibrillation and ventricular arrhythmias, and on using advanced imaging to guide treatment.
His published research includes MRI-guided electrophysiology and ablation, patient-specific computational modelling to predict ablation outcomes in persistent atrial fibrillation, the characterisation of atrial fibrosis and atrial cardiomyopathy, and tools for analysing electroanatomic mapping data.
His work has appeared in journals including Circulation: Arrhythmia and Electrophysiology, Europace and the Journal of Cardiovascular Electrophysiology. This research background informs his everyday practice: a detailed, evidence-based approach to diagnosing the cause of a patient’s symptoms and tailoring treatment to the individual. Known for his patient-centred approach, Dr Sim combines clinical excellence with clear communication to ensure patients feel informed, reassured, and supported throughout their care.
Reviewed regularly to reflect clinical best practice
Last reviewed: 25 June 2026
