SUMMARY

The trabecula septomarginalis of 30 dog hearts, aged between two and six years old, with no history of heart conditions were studied, aiming to characterize the number of insertions, dimensions, constitution and tissue arrangement of trabeculae. The knowledge about this structure should be used as a tool in morphophysiology studies and cardiac clinic-surgical procedures. Trabecula fragments underwent dehydration with ethanol, diaphanization in xylene, impregnation and were embedded in paraffin. Subsequently, prepared tissue fragments were cut into 5-µm-thick slices using a manual microtome (Leica RM 2125RT) and stained with modified Mallory trichrome. Photomicrographs were obtained using a digital optical microscope Zeiss Axioscópio and the images were analyzed by the image analysis software Zeiss KS-400. The data were subjected to Mann-Whitney U test. Macroscopically, the trabecula septomarginalis presented three types of insertion: simple (40%), double (33.33%) and branched (26.67%). Microscopically, the trabeculae septomarginalis consisted of striated cardiac muscle, connective tissue and cardiac conduction myofibers. The mean ratios plus standard deviations of connective tissue, striated cardiac muscle and cardiac conduction myofibers wer