The heart wears its blood vessels like a crown; hence the term “coronary”, first used in Renaissance Padua 500 years ago. Angina from obstructive coronary artery disease was described 250 years later in Enlightenment London. Yet the era of coronary physiology is quite recent, dating back only 50 years to the mid-1970s. The key insight was that, when an obstructive coronary artery is unable to double its blood flow to the subtended myocardium during stress, the coronary stenosis is physiologically significant and likely to cause ischaemia. Because direct coronary flow measurement was impossible in humans, clinicians instead relied on a pressure surrogate, the fractional flow reserve, to assess the severity of coronary lesions during hyperaemia, a state when flow and pressure are proportional. However, it is now clear that, even in the absence of blocked coronary arteries, cardiac ischaemia can still occur, purportedly due to coronary microvascular dysfunction, a condition that affects the small vessels of the heart. This realisation, which marks the next phase of coronary physiology, has been facilitated by the advent of bolus thermodilution, while continuous thermodilution offers a highly reliable absolute coronary flow measurement, crucial for unravelling the diverse mechanisms of angina with non-obstructive coronary arteries.