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To determine the relation between myocardial ischemic indexes on exercise testing and on ambulatory Holter recording, 60 patients with stable coronary artery disease who exhibited an ischemic response to both testing procedures were studied. All patients performed a Bruce protocol exercise test and underwent 24-hour Holter recording within 2 weeks without antianginal medications. Mean exercise duration was 7.4 +/- 2.8 minutes, mean heart rate at 1 -mm ST depression was 118 +/- 20 beats/min and mean maximal ST depression during exercise was 2.2 +/- 1 mm. During Hofter recording the average number of ischemic episodes was 4.7 +/- 2.6 per patient, mean duration of dally ischemia was 62 +/- S4 minutes, mean maximal ST depression was 3.2 +/- 1.3 mm and average heart rate at 1mm ST depression was 93 +/- 17 beats/min. Overall, the correlations between ischemic indexes on both testing procedures were very weak (mean r.sup.2 = O.Or4). The only exercise variable that had a significant correlation (p Thus, ischemic indexes on exercise testing cannot accurately predict ischemic indexes on ambulatory Holter recording in patients with stable coronary artery disease who exhibit ischemic changes on both tests. These findings indicate that a great portion of the variability of Holter ischemic indexes is dependent on factors other than those represented by exercise testing indexes, and that Holter recording in the ambulatory setting might provide clinically relevant information in addition to that obtained by exercise testing in selected subsets of patients. (Am J Cardiol 1991;68:176-180), Coronary artery disease is a condition in which the arteries supplying blood to the heart become clogged, usually with fatty atherosclerotic deposits. The resulting diminution of cardiac blood supply (myocardial ischemia) can cause pain and damage to the heart. During exercise, when the workload on the heart is increased, the ischemia is frequently made worse. The relationship between the prevalence of episodes of ischemia during standardized hospital exercise testing and during everyday activities is not known; it is assumed that the former predicts the latter with a reasonable degree of accuracy, but well controlled studies on which this assumption can be based have not been done. To further investigate the relationship between ischemia during exercise testing and during normal daily activities, a study was carried out involving 60 patients with documented, stable coronary artery disease, all of whom exhibited myocardial ischemia both during the course of everyday exercise and during formal exercise testing. Exercise testing lasted an average of 7.4 minutes, during which all patients exhibited ischemia (as indicated by characteristic changes in the electrocardiographic record). During 24-hour ambulatory monitoring of cardiovascular parameters, patients experienced ischemia for an average of 62 minutes (4.7 episodes per patient). Overall, the correlations between indices of ischemia in exercise-induced and spontaneous situations were very weak. Hence, ischemic indices on exercise testing do not accurately predict ischemic indices during everyday activities, and 24-hour ambulatory monitoring can provide useful clinical data which exercise testing does not yield. (Consumer Summary produced by Reliance Medical Information, Inc.)