About 20% of patients undergoing cardiac catheterisation with a clinical suspicion of coronary artery disease have normal coronary arteries. Amongst this heterogeneous population, a sub-group has been identified with several features in common; these features have been termed cardiac syndrome X.¹ This syndrome is generally defined as angina-like chest pain occurring in association with a positive exercise tolerance test (ETT) and/or positive myocardial perfusion scan and angiographically normal coronary arteries but in the absence of cardiovascular disease.² Despite an excellent prognosis in terms of survival, a significant proportion of these patients continue to experience long-term chest pain which can be disabling or poorly responsive to treatment and often undergo repeated hospital admissions.^3,4

The primary aim of treatment is symptomatic control. However, few of the pharmacological trials to date have evaluated the effects of treatment on chest pain or related symptoms as opposed to ECG evidence of ischaemia. The pathophysiology of cardiac syndrome X remains unclear and appears heterogeneous. Common to all patients, however, is anginal-type chest pain and an “ischaemic” response on stress testing in the presence of normal epicardial coronary arteries, suggesting an important role for dynamic small vessel constriction.

Angiotensin II (ATII) is a powerful vasoconstrictor involved in the control of coronary vascular resistance and …