(a) A single electrical wave produced by the heart's natural pacemaker spreads throughout the heart and induces a contraction. These waves normally occur about once every 0.8s.
(b) A spiral wave of electrical activity generated in the heart with a period of about 0.2s can produce the fast oscillations characteristic of an arrhythmia called tachycardia, which often directly precedes the onset of fibrillation.
(c) Multiple spiral waves produced by the breakup of a spiral wave can lead to the fast irregular oscillations characteristic of fibrillation. (Experimental movies courtesy of Richard Gray)

It has become widely accepted that the most dangerous cardiac arrhythmias are due to reentrant waves, such as the spiral waves illustrated in (c) of the above figure. These electrical waves circulate repeatedly through the tissue with higher frequency than the heart's pacemaker, thereby altering the heart's regular function and resulting in inadequate pumping. We and researchers at other institutions are continuing to investigate how arrhythmias develop and how they depend on the dynamics of individual cells and cardiac tissue structure in order to develop better methods for treating and preventing arrhythmias.