Key Points Coronary microvascular function testing using functional coronary angiography (FCA) is underutilized for patients with an unmet need. 92% of patients undergoing FCA had an abnormal coronary microvascular pathway identified and 39% had abnormalities in all pathways tested demonstrating the complexity of the microvasculature. Call to action: (1) standardize terminology and definitions in microvascular dysfunction; (2) standardize FCA protocols; 3) investigate the agreement and interaction between different measures of microvasculature function.