Exercise electrocardiography has relatively poor specificity and predictive accuracy for 3-vessel coronary artery disease (CAD) when conventional diagnostic criteria are used. However, electrocardiographic evaluation using linear regression analysis of the heart-rate (HR)-related change in ST-segment depression (ST/HR slope) is reported to accurately distinguish patients with from those without CAD, and to accurately separate patients with 1-, 2- and 3-vessel CAD. To assess the applicability of this method and to compare it with conventional interpretation, retrospective evaluation of 50 patients in whom exercise electrocardiography and coronary cineangiography had been performed for suspected CAD was conducted using a modified ST/HR slope analysis limited to leads V5, V6 and aVF. Eighteen patients had 3-vessel, 22 had 2-vessel, 6 had 1-vessel and 4 had no CAD. Standard electrocardiographic criteria (1 mm or more of horizontal or downsloping ST depression) identified 3-vessel CAD with a sensitivity of 78%, specificity of 56% and positive predictive value of only 50%. Peak ST/HR slope criteria (greater than or equal to 6.0 microV/beat/min) identified 3-vessel CAD with a sensitivity of 78%, specificity of 97% and positive predictive value of 93%. The overall test accuracy using measured peak ST/HR slope was 90%, compared with 64% for standard ST-depression criteria. In conclusion, analysis of the peak ST/HR slope can greatly improve the diagnostic accuracy of exercise electrocardiography, and further prospective study of this method is indicated.