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Mark O'Neill

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Doctor  Cardiology



Professor Mark O’Neill completed his undergraduate medical and postgraduate scientific training at University College Dublin and the University of Oxford before embarking on specialist medical and cardiology training in London.

In 2005, he undertook a specialist training fellowship in cardiac electrophysiology in Bordeaux with Professors Michel Haissaguerre and Pier Jais, specifically to develop expertise in catheter ablation of atrial fibrillation.

In October 2009, he joined St Thomas’ Hospital and King’s College London in the Department of Cardiology and School of Biomedical Engineering and Imaging Sciences. He was promoted to Reader in 2011 and Professor in 2014. He is the Departmental Lead for Arrhythmias in Adult Congenital Heart Disease, the Divisional research lead for electrophysiology and the Service lead for Cardiac Electrophysiology and Devices. He currently supervises five PhD students and has published over 250 peer-reviewed papers, books and proceedings in the field of arrhythmia medicine.

He is an internationally recognized expert in catheter ablation of atrial fibrillation and tachycardia. He founded the London Deanery Subspecialty Electrophysiology Training Programme in 2008 and is the South London Training Programme Director for Electrophysiology. He is an editorial board member of three specialist electrophysiology journals and a scientific programme committee member of the Heart Rhythm Society, the largest professional association in the field of arrhythmia medicine.

He sees patients privately at 78 Harley St and the Harley St. Clinic. He performs electrophysiological interventions for simple and complex arrhythmias using the very latest techniques and technologies at both the Harley St Clinic and St. Thomas’ Hospital, London where he is the Director of the Translational XMRI Cardiac intervention Research Facility.

Areas of interest
Palpitations; Atrial fibrillation ablation; Cardiac electrophysiology; Radiofrequency catheter ablation; Arrhythmias; Ablation; Arrhythmias in adult congenital heart disease; magnetic resonance imaging; Supraventricular tachycardia; Ventricular tachycardia;

Current NHS consultant posts held

2009 – present: Consultant Cardiologist and Professor of Cardiac Electrophysiology, St. Thomas’ Hospital and King's College, London

Research interests

My research group seeks to understand better the mechanisms which cause cardiac arrhythmias in humans, in particular atrial fibrillation. Our primary goal is to understand the mechanism specific to the individual patient so as to personalise the treatment to the patient rather than the disease.

There are a number of key areas:

Advanced imaging tools (MRI and CT) to assess individual patient predisposition to arrhythmia

Evaluation of ablation therapies using MRI.

Biophysical modelling of cardiac arrhythmia and its treatment

Personal interests

I enjoy reading biography and non-fiction accounts of human endeavour and achievement. I enjoy most sports, in particular football, running, swimming and sailing.

Awards received

1998 First class honours MB BCh BAO, 1998 Ruben Harvey RCPI prize, 1941 Medal and Gold medal in Medicine, University Gold medal(1998), Bequest for best performance in Surgical finals (1998), Colman Saunders medal in Paediatrics, Kirwan medal and prize & Dwyer Joyce Prize in Ophthalmology, Prizes in Physiology (1992), Biochemistry (1991) and Pharmacology (1992), Gold medal in anatomy (1991) First place in year, 5 of 6 years of UCD medical school 1992 Rhodes Scholarship, University of Oxford

(Additional) Languages spoken

  • English - Native or bilingual
  • French - Fluent


Over 100 peer-reviewed papers in cardiac electrophysiology, in addition to review articles, book chapters, conference proceedings and two books on catheter ablation of persistent AF.


  • English

Amenities and Features

  • Accepts Credit Cards
  • Family/Kids Friendly
  • Underground Station

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