Fir is the taxon subjected to the selection systems in Turkish forestry. In selection forests, targetdiameter is the main criterion for planning and management. In this study the aim is to determine theformation and level of the heart rot and target diameter depending on aspect and altitude for Abiesnordmanniana subsp. bornmülleriana Mattf. For this purpose, the fir trees with maximum diameters werecut and the situation of heart rot at various altitude levels (900-1,200 m, 1,200-1,500 m, and 1,500-1,800m) and aspects was determined. The formation of heart rot starts at low altitudes and this defect wasfound nearly on all fir trees of target diameter of 60 cm which is commonly used in practical Turkishforestry. Target diameter of 60 cm was considered as usable at the altitude of 1,200 m and even higher, at1,500 m and even more, the usable target diameter is more than 60 cm, as heart rot was not found in thesample trees with target diameters about 70-80 cm. In addition to this, heart rot was detected less in firtrees located on the south-facing slopes than on the north-facing slopes. The correlation coefficientbetween the basal diameter and heart rot was 0.631; it was 0.638 in the fir trees on the north-facing slopesand 0.696 on the south-facing slopes. According to these results, the target diameter of fir trees, which aredominant in selection forests, must be planned considering the altitude and aspect.