We could not agree more with Professor Spaan that coronary physiology is not “that simple”. Conversely, we hope Professor Spaan will agree that fractional flow reserve (FFR) is far and away the simplest and most robust tool that we as clinicians need for clinical decision-making about revascularisation in individual patients.

Delving too deeply into the details of coronary physiology reaches beyond the scope of a tutorial such as the “Education in Heart” series.1 For this purpose, readers are referred to textbooks on coronary flow2 and coronary pressure.3 We are well aware that …