Left ventricular hypertrophy (LVH), a target organ response in essential hypertension, is only weakly related to clinical measurements of blood pressure. To determine whether blood pressure measured under basal or stress conditions more closely determines LVH, we compared echocardiographic left ventricular mass index and relative wall thickness with clinical blood pressure and with 24 hr recordings (home, work, and sleep) in 19 normal subjects and 81 patients with mild hypertension. Only a weak correlation was observed in the entire group between left ventricular mass index and clinical measurements of systolic and diastolic blood pressure (r = .24, p < .02; r = .20, p < .05, respectively), which was only slightly improved by use of systolic and diastolic blood pressure readings taken in the home (r = .31, p < .005; r = .21, p < .05, respectively). Sleep and total 24 hr blood pressure also related poorly to left ventricular mass index. In contrast, substantially higher correlations existed between left ventricular mass index and systolic and diastolic blood pressure measured by portable recorder in 60 subjects at work (r = .50, p < .001; r = .39, p < .01, respectively). Similarly, work diastolic blood pressure bore the closest relationship to relative wall thickness (r = .59, p < .001). Home blood pressure readings taken on a work day also showed a moderate relationship with indices of LVH, whereas weaker correlations were found in employed subjects whose blood pressure was recorded on a non-workday, and no relationship between blood pressure and LVH existed in subjects who were not employed. We conclude that hypertensive LVH is poorly related to clinical or home measurements of blood pressure but that a substantially closer relationship exists between LVH and blood pressure during recurring stress at work and between LVH and home blood pressure on a workday. Thus hypertensive cardiac hypertrophy appears to be more closely related to blood pressure during stressful Circulation 68, No. 3, 470-476, 1983. NUMEROUS STUDIES have demonstrated that the risk of disease and death increases as blood pressure rises.'4 However, despite the consistency of this finding and its high statistical significance in large populations, the actual correlations between blood pressure measurements and the incidence of morbid events have generally been relatively low.'4 One possible explana-
