Coronary flow reserve is an important functional parameter to understand the pathophysiology of coronary circulation. Coronary flow reserve measurement is used to assess epicardial coronary stenoses or to examine the integrity of microvascular circulation. An appreciation of coronary physiology is an integral part of clinical decision-making for cardiologists treating patients with coronary artery disease. The pioneering research efforts of Dr Lance Gould, who explored the relationship between the anatomic severity of a stenosis and its flow resistance (59;60), have been transferred to...