The prevalence of electrocardiographic poor R-wave progression was estimated by reviewing all electrocardiograms recorded in Glasgow Royal Infirmary over a 2-week period. It was found to be higher in women (19% vs. 11%) than in men. To investigate one possible reason, the effect of chest electrode positioning in women was thereafter examined. Eighty four women were recruited to a study in which chest electrodes were placed strictly in adherence with recommendations of using the 4th and 5th intercostal spaces as references and also using the more widely adopted technique of placing electrodes V3 to V6 under the left breast. R wave amplitudes were compared in V3 to V6 from both sets of recordings. It was found that measurements recorded on the breast by electrode V3 have a significantly smaller R wave magnitude compared to corresponding measurements below the breast, the mean difference being 34 (95% confidence interval [CI] of 7 to 60) microvolts. For V5 and V6, the reverse is true with measurements taken on the breast being larger, on average, than those taken below the breast by 119 (95% CI of 87 to 152) and 134 (95% CI of 108 to 160) microvolts respectively. For V4, there was no significant difference. Seventeen women with poor R wave progression suggestive of old anterior myocardial infarction had clinical data examined from which it was determined that 11 had a history suggestive of myocardial infarction, ie, the positive predictive value was 65% (95% CI of 42% to 87%). It was concluded that positioning of electrodes beneath rather than on top of the breast was not responsible for the increased prevalence of poor R wave progression in women and that the criterion of isolated poor R wave progression was too nonspecific to be of clinical value.