Jonathan was born in Pontypridd and was educated at Pontypridd Boys Grammar and Coed-y-lan Comprehensive school. He trained at the Medical College of St Bartholomew’s Hospital qualifying in 1985. His cardiology training was in Bristol and Bath before returning to Cardiff to do research, then as Senior Registrar. In 1999 he was appointed as Senior Lecturer in Cardiology at the Wales Heart Research Institute, and also as part-time NHS cardiologist in Bridgend.

In 2005 he became a full-time NHS consultant in Bridgend. He was lead cardiologist between 2005-15 during which time the department expanded significantly to provide a comprehensive echo service, pacing service and diagnostic cardiac catheter lab. In 2008 he was part of the team that won a NHS Wales award for innovations in cardiology out-patient services. He became Medical Director at Princess of Wales Hospital from 2015 to 2018.

He is the immediate past-President of both the Welsh Cardiovascular Society and the Society of Physicians in Wales. He has worked in the Wales Cardiac Network since the end of 2018.