To describe the morphological variability of the pectinate muscles (PM) and crista terminalis (CT) in the right atrium, to evaluate the presence of a taenia sagittalis (TS), and to propose a simplified anatomical classification.

Forty-five adult human hearts without major macroscopic abnormalities were dissected following a standardized protocol exposing the CT and PM. Each specimen was documented with high-resolution photographs and independently analyzed by two cardiac surgeons. The orientation of muscular fibers, the presence and number of TS, and the degree of cross-over between bundles were recorded.

The CT was identified in all specimens. Three morphological patterns of PM organization were distinguished: type I (parallel fibers without TS), type II (parallel fibers with one or more TS), and type III (disorganized fibers with multiple cross-overs). Their respective frequencies were 33.3%, 46.7%, and 20.0%. A single TS was the most frequent configuration.

The PM of the right atrium show marked anatomical variability. The proposed three-type classification provides a simplified and reproducible framework for describing their organization. Beyond anatomical description, it may offer practical relevance for imaging interpretation, electrophysiological procedures, and open cardiac surgery, while providing a basis for future studies exploring the relationship between right atrial architecture and atrial arrhythmogenesis.