This video shows an example of simulated anatomical reentry. The view is of a sheet of simulated tissue with a hole in the middle. A wave of electrical activity continuously circles the hole. This is a stable phenomenon, particularly in this simulation. It should go on indefinitely, as long as I let the simulation keep going. Even in experimental set-ups (such as animal models) these can run for more than an hour.

In the video, black is tissue at rest, white/yellow tissue is activated, and red marks activation (at the front) and re-polarization (at the tail of the wave). If this happened around an obstacle in your heart, it would result in atrial flutter (if it occurred in your atria) or ventricular tachycardia (if it occurred in the ventricles). I’ll do a more extensive post in my “CEP Basics” pages later, but for now, here’s the video. The quality was great until YouTube crappified it.