Don't forget to hit load after you have selected one of the layouts.
This is a little applet designed to demonstrate the heart's electrical conduction system. You can play around and create your own conduction system. Note that the green squares are fast-conducting and the blue squares are slow-conducting. The blue squares also have a longer refractory period.
I have included a handful of systems I made. You can select the one you want to see in the box at the bottom and click "Load". They look a lot like the old Atari 2600 video games. When Fire is selected, clicking the mouse over a square will cause it to act like a pacemaker.
You can try a larger version here.
This applet requires the Java plug-in. You can download it for free by clicking on the following link :