A QRS scoring system for estimating the size of a myocardial infarct was evaluated in 55 patients who did not have left ventricular hypertrophy or conduction abnormalities. Serial 12-lead surface electrocardiograms were scored according to a 29-point system based on the duration of Q and R waves and on the ratios of R-to-Q amplitude and R-to-S amplitude. The scores were proportional to the severity of wall-motion abnormalities, which was determined by radionuclide blood-pool scanning and which correlated inversely with the radionuclide-determined left ventricular ejection fraction (LVEF). A score >3 was 93 per cent sensitive and 88 per cent specific for both severe regional dyssynergy and major depression of the global LVEF. The following equation was used to estimate the LVEF from the QRS score: LVEF (%) = 60 - (3 X QRS score). After acute myocardial infarction, an electrocardiogram can provide important indirect quantitative information about left ventricular function. (N Engl J Med. 1982; 306:4–9.), The major determinants of the immediate and long-term outcomes of acute myocardial infarction are the size of the infarct and the functional status of the residual myocardium.12345 The value of the electrocardiogram in diagnosing and localizing an acute myocardial infarct is well established; however, its use for measuring the size of an infarct or for assessing left ventricular function has not been well defined. A QRS scoring system based on computer simulation of the sequence of ventricular activation has been developed by Selvester and his associates.6789 The purpose of the study described here was to evaluate the usefulness of the. © 1982, Massachusetts Medical Society. All rights reserved.