Prof. Mark O'Neill, Cardiologist and Professor of Electrophysiology

Prof. Mark O'Neill DPhil, FRCP, FHRS, MRCP, MB BCh BAO

Cardiologist and Professor of Electrophysiology

DPhil, FRCP, FHRS, MRCP, MB BCh BAO
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Prof.Mark O'Neill,Cardiologist

Prof. O'Neill is a recommended Cardiologist and Professor of Electrophysiology

How do wearable devices like smart watches help heart rhythm experts?

How do wearable devices like smart watches help heart rhythm experts?

What is a heart palpitation and should I be worried?

What is a heart palpitation and should I be worried?

What is atrial fibrillation and is it dangerous?

What is atrial fibrillation and is it dangerous?

Prof. Mark O'Neill - Consulting

Prof. Mark O'Neill - Consulting

Areas of expertise

  • All arrhythmias
  • Atrial fibrillation
  • Catheter ablation
  • MRI
  • Clinical research
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Recommendations for Prof. O'Neill

These recommendations are for information purposes only. Doctors providing recommendations do so in good faith and are not responsible for clinical outcomes.

Recommended by:

  • byDr Samina Showghi, GP

    Over the 10 years I have known and referred to Mark, he always provides the best care clinically, technically and psychologically to my patients and my family – there is no higher recognition possible. The ‘cardiac electrician’ not to be missed!

  • byDr Brian Clapp, Cardiologist

    Prof Mark O’Neill is a very knowledgeable specialist within his field of Electrophysiology. He always provides a valuable opinion for patients that I refer to him and, if required, has a high level of technical ability when undertaking procedures. I am confident in recommending him to my patients.

  • byDr Matthew Wright, Cardiologist and Electrophysiologist

    Prof. Mark O'Neill really cares about individual patients and doing what's safe. He's technically excellent. If it was me, I'd have Prof. Mark O'Neill operate on me.

  • by Dr James Harrison, Cardiologist

    Prof. Mark O'Neill is an outstanding clinician, who always provides an excellent opinion for patients with heart rhythm problems. He is an international expert in atrial fibrillation and I have no hesitation in recommending him to my patients.

  • by Dr Sonja Meier, Pain Medicine Specialist

    He is exceptionally professional, compassionate and engaged. I would always recommend him to my friends and family!

  • byDr Samina Showghi, GP

    Over the 10 years I have known and referred to Mark, he always provides the best care clinically, technically and psychologically to my patients and my family – there is no higher recognition possible. The ‘cardiac electrician’ not to be missed!

  • byDr Brian Clapp, Cardiologist

    Prof Mark O’Neill is a very knowledgeable specialist within his field of Electrophysiology. He always provides a valuable opinion for patients that I refer to him and, if required, has a high level of technical ability when undertaking procedures. I am confident in recommending him to my patients.

  • byDr Matthew Wright, Cardiologist and Electrophysiologist

    Prof. Mark O'Neill really cares about individual patients and doing what's safe. He's technically excellent. If it was me, I'd have Prof. Mark O'Neill operate on me.

  • by Dr James Harrison, Cardiologist

    Prof. Mark O'Neill is an outstanding clinician, who always provides an excellent opinion for patients with heart rhythm problems. He is an international expert in atrial fibrillation and I have no hesitation in recommending him to my patients.

  • by Dr Sonja Meier, Pain Medicine Specialist

    He is exceptionally professional, compassionate and engaged. I would always recommend him to my friends and family!

  • Address

  • Telephone or video consultation

    Available for patients, please call to arrange, GB, W1G 7HR

  • The Heart Rhythm Clinic

    88 Harley Street, Marylebone, London, GB, W1G 7HR

  • The Harley Street Clinic

    35 Weymouth Street, London, GB, W1G 8BJ

  • Guy's Hospital (NHS)

    Great Maze Pond, London, Greater London, SE1 9RT

  • St Thomas' Hospital (NHS)

    Westminster Bridge Road, London, Greater London, SE1 7EH

  • About Prof. Mark O'Neill

    GMC number: 4636126

    Year qualified: 1998

    Place of primary qualification: University of Dublin

    Prof. 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 is the Departmental Service Lead for Cardiac Electrophysiology & Devices, the Clinical Lead for arrhythmias in Adult Congenital Heart Disease and the Divisional Research Lead for Electrophysiology. His primary research interests are the development and use of advanced signal processing and imaging technologies to improve arrhythmia characterization and treatment in patients with heart rhythm disturbances.

    Prof. O’Neill graduated from University College Dublin Medical School in 1998. His medical degree was intercalated with a physiology doctorate (DPhil), which he completed at Oxford University as a Rhodes Scholar (1992-1995). He trained in London in general medicine and cardiology, followed by subspecialty training in interventional cardiac electrophysiology at St Mary’s Hospital. From 2005-2006, he completed a clinical research fellowship in Bordeaux with Professors Michel Haïssaguerre and Pierre Jaïs where he gained particular expertise in atrial fibrillation.

    Prof. O’Neill has served on the Council of the British Heart Rhythm Society and on the Programme Committees of the major US (Heart Rhythm Society) and European (EHRA and Cardiostim) arrhythmia and electrophysiology scientific conferences, to which he contributes annually and extensively. He is the immediate Past President of the Cardiology Section of the Royal Society of Medicine where, over the course of the last decade, he established a successful pan-London training programme in cardiac electrophysiology and devices, and oversaw the delivery of more than 50 Training Days covering all aspects of cardiac rhythm management.

    Prof. O’Neill’s primary research interests are the development and use of advanced signal processing and imaging technologies to improve arrhythmia characterization and treatment in patients with heart rhythm disturbances. As well as lecturing both nationally and internationally on atrial arrhythmia management, he continues to publish widely and currently supervises four PhD students, two post-doctoral trainees and three clinical trainees in aspects of cardiac rhythm management within the School of Biomedical Engineering and Imaging Sciences at King's College London and the Electrophysiology Training programme at Guy's and St. Thomas' NHS Foundation Trust.

    Prof. O’Neill is passionate about imparting an evidence-based training and education for aspiring cardiac electrophysiologists and allied professionals, thereby ensuring that patients with heart rhythm disorders will always have early and direct access to the correct specialists in the appropriate environment for the best management of their condition.

    Areas of expertise

    • All arrhythmias
    • Arrhythmias in adult congenital heart disease
    • Atrial fibrillation ablation
    • Cardiac electrophysiology
    • Atrial tachycardias
    • Bradycardia
    • Syncope
    • Heart rhythm disorders
    • Vasovagal syncope
    • Catheter ablation
    • Clinical research
    • MRI
    • Atrial septal defect
    • Patent foramen ovale
    • Palpitations
    • Radiofrequency catheter ablation
    • Supraventricular tachycardia
    • Ventricular tachycardia
    • Dizzy spells and blackouts
    • General cardiology
    • Wolff–Parkinson–White syndrome (WPW)

    Frequently asked questions

  • What are the common symptoms that your patients tend to present with?

    It's quite varied. If the patient has been appropriately referred, it is usually because of palpitations. That's the most common symptom among the patients that I would see.

    Patients may also be referred with dizzy spells, breathlessness, lightheadedness, or even loss of consciousness. Oftentimes, patients will have researched their symptoms online in advance and will have decided that they should visit a doctor. Ectopic beats are a common symptom for which patients self-refer.

    Sometimes a specific arrhythmia diagnosis has been made or suspected elsewhere and the patient has been referred for specialist arrhythmia-focused investigation and management. The most common confirmed diagnosis made elsewhere and for which I am referred patients is atrial fibrillation. Less common but very amenable to curative treatment is an ECG-confirmed diagnosis of either atrial flutter or supraventricular tachycardia.

    Some patients may have a family history of heart troubles and they just want to be checked out to make sure they don’t have the same problem.

  • What are the treatments that you're able to offer your patients?

    At The Heart Rhythm Clinic, we can investigate and treat every form of heart rhythm disorder. The treatments break down into two broad categories – those for bradycardia (excessively low heart rates) and tachycardia (excessively high heart rates). For bradycardia, the treatment may be implantation of a pacemaker; for tachycardia, the treatments options are broader and depend really very much on the diagnosis. This could vary from medication to catheter ablation to implantation of a defibrillator.

    The majority of our work is seeing patients who have symptoms, but who don’t necessarily need an intervention and distinguishing those from the patients who do need an intervention, or whose quality of life could be improved by considering one.

    The most common intervention by far that we perform is catheter ablation for atrial fibrillation which is not surprising as this is the most common heart rhythm disturbance!

  • What are your areas of sub-specialist interest?

    Our practice is built on a strong academic base. The consultant members of The Heart Rhythm Clinic are engaged in ongoing research into the conditions that we ultimately treat in patients, particularly atrial fibrillation. We have a very broad-reaching research portfolio to investigate mechanisms of atrial fibrillation, but also to identify the patients who would benefit most from intervention and hopefully to avoid invasive treatments in patients where the likelihood of arrhythmia cure is low.

    Atrial fibrillation is a blunt diagnosis, made on the basis of a single heart rhythm ECG recording but actually it represents a spectrum of electrical disorder of the heart. So, being able to tailor appropriately the investigation and management to the patient in front of us is very important. I would argue that this is something we do very well, helped in part by our extensive research work (over 250 peer-reviewed journal papers) specifically in the investigation and management of atrial fibrillation.

    We also have strong links with cardiac imaging, bioengineering, and computational modelling to support our research in atrial fibrillation. Although we are electrophysiologists, we have access to expertise in these complementary fields that permits us to offer something beyond standard electrophysiological practice. Whether that makes us better or not, I don’t know, but it certainly makes us evidence-based and unlikely to offer treatment on the basis of gut feeling or tradition!

    The investigation and treatment our patients receive are based on the most contemporary data in the field of arrhythmia medicine and where appropriate, our own published work.

  • Professional memberships

    Heart Rhythm Society
    European Heart Rhythm Association
    British Heart Rhythm Society
    General Medical Council
    Independent Doctors Federation grayscale

    Articles by Prof. Mark O'Neill

    Atrial Septal Defects and Patent Foramen Ovale

    Other specialists recommended by Prof. O'Neill

  • Dr Brian Clapp, Cardiologist

    Dr Clapp is a pragmatic, conscientious cardiologist who always acts in the best interests of his patients. In addition to his expertise in interventional cardiology, he has a broad scope of practice in general cardiology and offers a very high quality opinion which is why I have been referring patients to him for the last ten years. I have no hesitation in recommending him.

  • Dr Matthew Wright, Cardiologist and Electrophysiologist

    Dr. Wright is a highly competent cardiologist and electrophysiologist. He always puts the patient first; his constant attention to improvement coupled with his high level of technical expertise make him one of the best heart rhythm opinions in the country.