Professor Mark O'Neill

Professor Mark O'Neill



Recommended by 3 specialists
24 years of experience
14 years as a specialist

Overall Rating

Overall Experience


Bedside Manner




Top feedback

“Excellent, frequency of visits much welcomed. Clarity on next steps of treatment also excellent. “
Read more


  • Electrophysiology
Show more

Languages spoken

  • English
  • French
Show more

Registered with

  • General Medical Council: 4636126
Show more

    Consultation fees

    New appointment: £300

    Follow-up appointment: £160

    Practices worked at

    London Bridge Hospital

    27 Tooley Street, London, United Kingdom, SE1 2PR
    2,775 reviews

    The Harley Street Clinic

    35 Weymouth Street, london, United Kingdom, W1G 8BJ
    1,764 reviews

    Specialist's working hours

    Not available
    Not available
    14:00 - 19:00
    Not available
    Not available
    Not available
    Not available


    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)
    • CT Coronary Angiogram
    • Calcium Coronary Score
    • 24 Hour Blood Pressure Monitor
    • Cardiac MRI
    • Cardioversion
    • ECG Monitor
    • Echocardiogram
    • Health Assessments
    • Heart & Lung Health Assessments
    • Heart Scan
    • Stress Echocardiogram
    • Transoesophageal Echocardiogram
    • Video Consultation
    Read more

    Special interests

    • Atrial Fibrillation
    • Arrhythmia (Irregular Heartbeat)
    • Palpitations
    • Breathlessness
    • Tachycardia
    • Adult Congenital Heart Disease
    • Atrial Flutter
    • Bradycardia
    • Chest Pain
    • Dizziness
    • Fainting
    • Heart Attack
    • Loss of Consciousness (Syncope)
    • Supraventricular Tachycardia (SVT)
    • Ventricular Fibrillation
    Read more


    • 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
    Read more


    Powered by Doctify
    Promoting trust & transparency in healthcare