Acetylcholinesterase (AChE), the enzyme that degrades acetylcholine, exists as a multiple molecular forms that differ in their quaternary structure and mode of attachment to the cell surface. The distribution of the individual molecular forms of AChE in various cardiac regions with distinct anatomical characteristics was investigated. The results confirmed those of others by showing that the total pool of cardiac AChE had a nonuniform distribution in heart that paralleled the distribution of choline acetyltransferase. The rank order of this distribution was right atrial appendage greater than interatrial septum greater than left atrial appendage = right ventricle = interventricular septum greater than left ventricle. Velocity sedimentation in sucrose gradients of extracts from selected cardiac areas showed that four molecular forms were present in all areas but that the proportions of these forms differed as a function of area. The right and left ventricular walls, the apical portion of the interventricular septum, and the left atrial appendage contained G1 and G4 (globular) AChE in near-equal proportions, but in the basal portion of interventricular septum, the contribution of G4 AChE was greater than that of G1 AChE. The right atrial appendage and the interatrial septum had the largest amount of activity attributable to G4 AChE and the lowest amount attributable to G1 AChE. In all cardiac regions, A12 (asymmetric) AChE comprised 8-10% of the total AChE pool.(ABSTRACT TRUNCATED AT 250 WORDS)