A subset of patients with chest pain and normal coronary angiograms are believed to have coronary microvascular dysfunction which limits coronary flow reserve. In order to assess whether pharmacologic measures of coronary flow reserve correlate with responses of the left ventricle to stress, we measured coronary flow velocity in the left main coronary artery of 27 patients with chest pain and normal coronary angiograms and normal left ventricular function at rest. The increase in coronary flow velocity over baseline following adenosine, a potent coronary microvascular vasodilator in 10 patients with abnormal left ventricular responses to exercise by radionuclide angiography was no different from that of 17 patients with normal left ventricular responses to exercise. However, repeat assessment of coronary flow reserve following ergonovine .15 mg intravenously showed a decline in coronary flow velocity response to adenosine in the 10 patients with abnormal left ventricular responses to exercise in contrast to no change in the 17 patients with normal left ventricular responses to exercise. Thus, pharmacologic assessment of coronary flow reserve before and following ergonovine suggests dynamic rather than fixed abnormality of coronary microvascular function is associated with abnormal left ventricular responses to exercise in patients with chest pain despite normal coronary angiograms.