Sir,—Owing to the age related prevalence of coronary heart disease (CHD), the observation that angiographically validated CHD is more common in patients aged ⩾ 55 with “atypical” chest pain than in their younger counterparts,1 and that this is true for women aged ⩾ 52 with negative exercise tolerance tests and ⩾ 3 risk factors for CHD,2 is a validation of the proposition, consistent with Bayes’s theorem, that the higher the prevalence of any disease, the greater the likelihood of atypical presentation. This is a concept that deserves more universal recognition to circumvent omissions of the type exemplified by a recent evaluation (among other considerations) of the diagnostic role of non-invasive nuclear imaging in patients with intermediate likelihood of CHD.3 This study did not test the hypothesis that the predictive accuracy of nuclear imaging could be age related. In the absence of such information, especially in view of the documentation of poor negative predictive value for the exercise tolerance test,3 the threshold for angiographic investigation should be lower in the old than in the young, especially in view of the necropsy validation of an age related increase in severity of individual coronary atherosclerotic lesions.4