A 53-year-old female presented with disabling chest pain. The pain had most of the characteristics of ischemic pain; however, the results of the initial clinical investigation were consistent with the diagnosis of syndrome X. That is, her treadmill exercise test was positive but her coronary angiogram was normal. A dipyridamole-thallium test resulted in severe chest pain, marked ST abnormalities, but no evidence of any focal reduction in flow. A dipyridamole stress echocardiogram revealed that left ventricular function was entirely normal during the dipyridamole-induced pain and ST segment abnormalities, making ischemia an unlikely cause for either. To attempt to account for this paradox, the hypothesis was generated that both the pain and ST segment abnormalities were due to a primary abnormality of adenosine metabolism rather than secondary to ischemia. Accordingly, adenosine-MIBI scans were done with and without pretreatment with aminophylline. Infusion of adenosine virtually immediately resulted in crushing chest pain and profound ST abnormalities again without any evidence of focal abnormalities of MIBI estimated flow. By contrast, administration of adenosine after pretreatment with aminophylline failed to produce either chest pain or ST abnormalities. Moreover, long term therapy with aminophylline almost entirely relieved the symptoms which had been so distressing. This case indicates that there is a subset of patients with syndrome X--in which faults in adenosine metabolism result in excessive adenosine accumulation or effect and this results, in turn, in adenosine-induced ischemic-like chest pain and adenosine-induced ST abnormalities. There is, however, no actual ischemia of the myocardium. Given the known effects of adenosine on coronary flow, the problem in this subset of patients appears to be equivalent to an attack of myocardial migraine and blockers of adenosine action might be of help to other patients with a similar pathophysiology for their chest pain.