Rapid development of interventional procedures for treating cardiacarrhythmias, especially transcatheter ablation, reveals a renewed interest inheart morphology. Mitral isthmus is one of the main target for atrialfibrillation ablation. Ablation within the cavotricuspid area is the method ofchoice for treating atrial flutter. Is this study we examined 200 autopsiedhuman hearts.The mean mitral isthmus length was 28.8mm. In 34.5% of all cases crevicesand diverticula, intertrabecular recesses or trabecular bridges could beobserved. The great cardiac vein was present within the isthmus in 98.0%and the left circumflex artery in 57.0%. In 16.7% of cases the left circumflexartery was located closer than 2mm from the endocardial surface of the leftatrium, and in 49.1% closer than 3mm. We were able to detect eight differentpatterns of mutual blood vessels arrangement within the mitral isthmus line.We proposed the left atrial appendage isthmus line (between the margin ofthe left atrial appendage orifice and the margin of the mitral annulus) forpotential clinical use. This area have favorable anatomy and could beclinically used as a target for catheter ablation.We have created an anatomical model of the cavotricuspid isthmus areawhich can be helpful in performing electrocardiological procedures. Thepresence of intertrabecular recesses (25.0%), trabecular bridges (12.9%) andsub-Eustachian recesses (48.6%) within the cavotricuspid isthmus can makeablation more difficult. We have presented the macroscopic patterns of finalramifications of the terminal crest within the isthmus (10-step classification).