The effects of acute myocardial infarction (MI) on the displacement of the left ventricular (LV) atrioventricular (AV) plane is presented. The material consisted of 40 patients with first-time Q-wave MI (26 pts with ant. MI and 14 with post. MI). Nineteen age-matched healthy subjects were used as controls. The displacement of the AV plane was determined at four sites corresponding to anterior (AV-A), septal (AV-S), posterior (AV-P) and lateral (AV-L) parts of the LV wall. In anterior and posterior MI all the sites showed significantly reduced AV-plane displacement compared to healthy subjects (P less than 0.001). Moreover, within the anterior MI group the AV-A and AV-S displacements were significantly reduced compared to the points AV-L and AV-P (P less than 0.001) and the AV-L displacement was reduced compared to AV-P (P less than 0.001). In posterior MI the displacement at AV-P was reduced compared to other points (P less than 0.001) and, to a certain extent, AV-S was reduced compared to the points AV-A and AV-L (P less than 0.001). The reduced magnitude of the AV plane displacement seems to be an expression of regionally reduced systolic function. The method described may provide a simple means of defining regional wall motion abnormalities of the LV following MI.