Magnetic resonance velocity vector mapping was used to study flow patterns in dilated and healthy left ventricles. Eleven patients (age mean +/- SD, 57 +/- 12 years) with dilated left ventricle resulting from coronary artery disease and 10 healthy volunteers (age 50 +/- 9) were studied. Cine gradient echo images were acquired in the left ventricle vertical and horizontal long axes. Vertical and horizontal velocity components in the horizontal long axis plane of the left ventricle were encoded simultaneously. Maps of velocity components were then processed into multiple computer generated streaks whose orientation and length corresponded to velocity vectors. The following parameters (mean +/- SD) differed significantly between the two groups: The heart rate (patients 70 +/- 11 beat/min. controls 57 +/- 8, P < .001), end-diastolic volume (patients 264 +/- 83 ml, controls 143 +/- 25 ml, P < .001), ejection fraction (patients 31% +/- 7, controls 61% +/- 5, P < .001), diameter of the inflow stream (patients 1.7 +/- 0.6 cm, controls 3.2 +/- 0.3 cm, P < .001). In normal subjects the predominant direction of diastolic flow through the mitral valve was toward the apex, with short-lived vortices curling back behind each mitral leaflet. The vortex beneath the anterior leaflet tended to be larger and more dominant. In patients with dilated left ventricle, the inflow was directed toward the free wall, giving rise to a well developed circular flow pattern turning back toward the septum and outflow tract and persisting through diastole. Magnetic resonance velocity vector mapping is an excellent method for studying left ventricular flow patterns.(ABSTRACT TRUNCATED AT 250 WORDS)