Professor Mark O'Neill

Professor Mark O'Neill



22 years of experience
13 years as a specialist

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“Professor O'Neill is a wonderful physician - he is caring, thoughtful, incredibly thorough and clear communicator. I trust him completely with my cardiac health and would recommend anyone with an electrophysiology concern to see him. The support team, including Aaliyah and Karmen are also super helpful and friendly! “
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  • Electrophysiology
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Languages spoken

  • English
  • French
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Registered with

  • General Medical Council: 4636126
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    Consultation fees

    New appointment: £250

    Follow-up appointment: £150

    Practices worked at

    The Harley Street Clinic

    35 Weymouth Street, london, United Kingdom, W1G
    1065 reviews

    The Heart Rhythm Clinic

    88 Harley Street, Marylebone, United Kingdom, W1G 7HR
    6 reviews


    Professor Mark O’Neill is a Consultant Cardiologist and Electrophysiologist at St. Thomas’ Hospital London and Professor of Cardiac Electrophysiology at King’s College London. He qualified with first class honours from University College Dublin Medical School in 1998, having completed his DPhil in Cardiac Physiology as a Rhodes Scholar at Oxford University in 1995. He undertook subspecialty training in interventional cardiac electrophysiology at St Mary’s Hospital and in 2005  undertook a British Heart Foundation fellowship in the world-renowned arrhythmia centre in Bordeaux where he gained particular expertise in catheter ablation of atrial fibrillation. 

    He joined St Thomas’ Hospital and King’s College London as a consultant in the Department of Cardiology and Division of Imaging Sciences and Biomedical Engineering in 2009. He was promoted to Reader in 2011 and Professor in 2013 and has since led the arrhythmia service, regional training programme and divisional research programme in cardiac electrophysiology. In 2016, in recognition of the quality and breadth of his clinical and academic work, he received a National Bronze Clinical Excellence award.

    Professor O'Neill is an international opinion leader in cardiac electrophysiology, is actively involved in research and has published over 200 papers in peer-reviewed journals. His research addresses the mechanisms of atrial fibrillation and the use of novel mapping, imaging and computational modelling techniques to better understand the reasons why a patient develops AF and therefore how best to manage it. 

    He lectures regularly in the UK and abroad on atrial arrhythmia management. He treats patients with simple and complex heart rhythm disturbances of atrial and ventricular origin, in particular atrial fibrillation and tachycardia in the context of inherited and acquired structural heart disease.

    His private practice is based at The Heart Rhythm Clinic, 88 Harley Street. He performs interventional electrophysiology procedures at the Harley St Clinic.

    In June 2018, the Daily Mail published the profiles of the top ten UK electrophysiologists recommended by cardiologists themselves. About Professor O'Neill, his peers were quoted as saying: "On the leading edge, he has built an international reputation based on his prolific research work. He is also known to provide a measured opinion on what is best for patients. He is an extremely astute doctor, particularly in diagnostics. He will look at patients very objectively and pick up very subtle clinical signs that others will overlook."

    At the Heart Rhythm Clinic, Professor O'Neill will give you the time to help you understand your symptoms and reach a diagnosis. He will provide treatment advice and expertise in partnership with you and tailored to your concerns.

    Diseases, Medical Tests and Treatments
    • Catheter ablation
    • AF ablation
    • Pulmonary vein isolation
    • Electrophysiology Study
    • DC Cardioversion
    • Implantable Loop Recorder
    • Ambulatory heart rhythm monitoring (1-14 days)
    • Atrial fibrillation
    • Atrial tachycardia
    • Atrial flutter
    • Arrhythmia in adult congenital heart disease
    • Supraventricular Tachycardia
    • Ventricular Tachycardia


    • ECG (Electrocardiogram)
    • 24 Hour Blood Pressure Monitor
    • CT Coronary Angiogram
    • Calcium Coronary Score
    • Cardiac MRI
    • ECG Monitor
    • Echocardiogram
    • Transoesophageal Echocardiogram
    • Video Consultation
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    Special interests

    • Arrhythmia (Irregular Heartbeat)
    • Atrial Fibrillation
    • Palpitations
    • Tachycardia
    • Adult Congenital Heart Disease
    • Bradycardia
    • Dizziness
    • Loss of Consciousness (Syncope)
    • Ventricular Fibrillation
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    • FRCP - Royal College of Physicians - 2012
    • FHRS - Heart Rhythm Society 2011
    • MRCP - Royal College of Physicians - 2001
    • MB BCh BAO (first-class honours) - University College Dublin - 1998
    • DPhil in Physiological Sciences, Rhodes Scholar - University of Oxford - 1995
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