In 2003 he was appointed as Consultant Cardiologist at King’s College Hospital and Hon. Senior Lecturer in Cardiology at King’s College London School of Medicine.
He was responsible for the development of the primary angioplasty service at King’s and is the lead cardiologist in the very successful trans-catheter aortic valve (TAVI) programme. He has served as an international Proctor for TAVI and taught 14 UK Teaching Hospitals the technique.
In 2007, Prof MacCarthy was appointed Clinical Lead in Cardiology at King’s College Hospital and in 2012, Clinical Director of Cardiovascular Services at King's.
In 2014 he was promoted to Professor of Interventional Cardiology, King's College London. In 2016 he was appointed the King’s Clinical Lead for the KHP Institute programme. He is a member of BCIS Council and Chair of the BCIS Structural Working Group.
His research interests include applied coronary physiology/endothelial function, LV haemodynamics and emerging interventional therapy (including trans-catheter valve therapy and primary angioplasty).