Forty-nine normal children underwent echocardiography to study the role of automatic border detection (ABD) in diastolic evaluation by (1) determining the relationship of diastolic ABD indexes to heart rate and traditional diastolic indexes and (2) establishing inter-observer variability. ABD diastolic indexes were less associated with heart rate than were M-mode and Doppler diastolic indexes. ABD left ventricular peak filling rate correlated with Doppler mitral E wave peak velocity. Interobserver variability for ABD indexes ranged from 4% to 24%. We then compared the ability of ABD left ventricular filling rate to M-mode and Doppler indexes to detect diastolic dysfunction in a test group of 20 children with diastolic disease. ABD left ventricular peak filling rate had the highest sensitivity of all indexes (90%). Thus ABD left ventricular peak filling rate is an accurate index of diastolic function that is readily usable by almost all clinical laboratories.