Welcome to the introductory segment of Dr Robert Jay Widmer's 'Cath Lab Guide to Coronary Reactivity Testing in Non‑Obstructive CAD'. 

Dr Widmer (The McKinney Heart Hospital, US) presents the case of a 25-year-old female endurance runner experiencing exertional, band-like chest pain. Her coronary CTA appears normal, while PET imaging reveals mildly reduced flow confined to the circumflex territory.

Dr Widmer reviews the patient's prior treadmill test results, empirical anti-anginal therapy, and the diagnostic considerations—balancing the possibilities of coronary microvascular dysfunction and pericarditis in a young patient with no evidence of obstructive CAD. The discussion frames the clinical rationale for proceeding to invasive coronary function testing, even when non-invasive imaging appears reassuring.

Key learning points:

• Identifying red flags for INOCA/ANOCA in young, low-risk patients with persistent chest pain despite normal CTA findings.
• Interpreting “borderline” versus abnormal PET-derived myocardial blood flow and MFR, and understanding how these results guide further evaluation.
• Constructing a focused differential diagnosis—considering microvascular dysfunction, vasospasm, pericarditis, and non-cardiac causes—before deciding on catheterization.