Figure 4.

Schematic illustration of a figure-of-eight reentry. A wavefront approaches two obstacles separated by a small gap of low excitability (gray area). Conduction is blocked in front of this gap, separating the wavefront. Behind the obstacles, wavefront collision occurs. This increases the current source while reducing the sink and, thus, allows activation of the area between the obstacles. If conduction is slow enough, this leads to reentry in front of the obstacles as shown by el-Sherif et al. (1987).