Regional function assessed by ventriculography may be influenced by the hemodynamic effects of rapidly injecting ionic contrast medium. The importance of this after acute coronary occlusion was examined in eight open-chest, anesthetized dogs. The left anterior descending artery was ligated while sonomicrometric segment lengths in the ischemic (IZ) and nonischemic zones (NZ) were measured. Sodium methylglucamine diatrizoate (Renografin-76, 1 ml/kg) was rapidly injected over 3 seconds. Fifteen minutes later, the left ventricular end-diastolic pressure (LVEDP) was rapidly increased to the level reached during injection. Injecting the contrast increased the LVEDP (7.3 +/- 2.5 to 20.1 +/- 2.9 mm Hg, p less than 0.0001) to the same extent as raising LVEDP (7.6 +/- 2.5 to 10.1 +/- 2.9 mm Hg, p less than 0.0001). Injecting the contrast medium increased IZ total percent systolic shortening (% delta L) (-3.90 +/- 4.43% to -2.68 +/- 4.77%, p less than 0.001) by decreasing isovolumic bulging (-6.68 +/- 4.09% to -5.49 +/- 3.33%, p less than 0.001) with little change in ejection % delta L. NZ total % delta L tended to increase (19.03 +/- 6.53% to 19.94 +/- 6.27%, p = 0.015) because of augmented ejection % delta L (13.12 +/- 2.51% to 13.71 +/- 3.10%, p = 0.017) by the Starling mechanism. Increasing the LVEDP had the same effect on IZ and NZ regional shortening as injecting contrast. Thus regional shortening after acute coronary occlusion is affected by the changes in loading conditions with ionic contrast ventriculography.(ABSTRACT TRUNCATED AT 250 WORDS)