**6.1 Normal atrioventricular bundle**

The normal variant (type I) was in 49 subjects out of 105 (46.7%). The atrioventricular bundle (the HB) coursed along the lower border of the membranous part of the IVS and was covered by a thin layer of common myocardial fibers spanning from the muscular part to the membranous part of the IVS (**Figure 3**). Fusion phenomenon was seen during HBP in this anatomical variation, or non-selective HBP in higher current amplitude and selective HBP in lower current amplitude during pacing.
