Recent new information on the dynamics and molecular mechanisms of electrical rotors and spiral waves has increased our understanding of both atrial fibrillation and ventricular fibrillation. In this brief review, we evaluate the available evidence for the separate roles played by individual sarcolemmal ion channels in atrial fibrillation and ventricular fibrillation, assessing the clinical relevance of such findings. Importantly, although human data support the idea that rotors are a crucial mechanism for fibrillation maintenance in both atria and ventricles, there are clear inherent differences between the 2 chamber types, particularly in regard to the role of specific ion channels in fibrillation. But there also are similarities. This knowledge, together with new information on the changes that take place during disease evolution and between structurally normal and diseased hearts, may enhance our understanding of fibrillatory processes pointing to new approaches to improve disease outcomes.