Dr Mason has considerable experience in a wide spectrum of Cardiology.  His main area of interest is in the investigation and management of patients experiencing dizziness or blackouts, patients with weakened hearts who are at risk of or who have experienced potentially life-threatening rhythms, and the assessment and management of patients with weakened hearts who may benefit from pacing for heart failure.  He is a nationally and internationally recognised expert in the implantation of pacemakers, implantable cardioverter defibrillators (ICDs) and biventricular pacemakers and ICDs (CRT).  These are collectively known as Cardiac Implantable Electronic Devices, or CIEDs.  He is also an expert in the removal of pacemakers and ICDs, when necessary, including the use of laser extraction techniques and was a specialist adviser to NICE on this area.  Dr Mason retains a substantial interest in the investigation and management of patients with coronary artery disease, including the performance of coronary angioplasty and stenting and has played a pivotal role in the delivery of the primary angioplasty service for acute heart attacks at Harefield Hospital since 2004.

He has lectured extensively at international meetings on both CIEDs and coronary angioplasty.  He has been part of policy setting groups for CIED therapy, and was part of the National Infarct Angioplasty Project (NIAP) which pioneered coronary angioplasty for treating UK patients having heart attacks (myocardial infarction).