In order to study whether different heart rates achieved at peak exercise by normal subjects and patients with coronary artery disease (CAD) affect the results of analysis of R-wave amplitude changes (delta R), we evaluated delta R at progressively increasing heart rate (HR) steps in 60 normal subjects with negative exercise tests (ET), in 130 patients with CAD, in 88 patients with true positive and 42 with false negative ET, and in 43 patients with no CAD and false positive ET. We found that the sensitivity and specificity of delta R were HR dependent, the former decreasing and the latter increasing with progressively increasing HR steps. Mean values of delta R did not discriminate among the four groups for HRs up to 150 bpm; significant differences were found between normal subjects and CAD patients, both with true positive and false negative stress tests, at HR greater than 150 bpm. False positive patients had mean delta R similar to those found in normal subjects. We hypothesize that quantitative delta R analysis could be useful in ECG diagnosis of false negative and false positive patients at HR greater than 150 bpm.