This report was an overview of pacing therapy for heart failure to explain the usefulness and problems of CRT in broad terms. It is not an exaggeration to say that pacemakers were originally developed to improve cardiac function in patients with heart failure. However, it must be understood that pacing itself is unphysiological, and we should know what pacing does to the heart. Concerning the simple issue of pacing, it is true that there are a lot of matters that we think we understand but actually we do not, such as the effects of the differences in site, output, and frequency. At least, it seems clear that the currently available CRT devices are effective for patients with heart failure and for improving survival. Further improvement in their effectiveness is an important issue we must continue to address.

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