The last of an ongoing series of Cardiostim monographs all devoted to cardiac pacing, was published four years ago. Since then, cardiac res- chronization for the treatment of heart failure has undergone spectacular progress and has revolutionized device therapy. Many patients have benefited from ventricular resynchronization often combined with an implantable cardioverter-defibrillator. More implantations are likely in the future as the indications continue to evolve with more attention being paid to the primary prevention of heart failure in selected patients and the treatment of earlier stages of left ventricular dysfunction. Thus, we felt it was time for the current Cardiostim monograph to focus exclusively on cardiac resynchronization so as to review the remarkable technologic and clinical advances in the field. We are grateful to the contributors who worked so hard to complete their manuscripts on time and their diligence in presenting new concepts and technical details in an easily understandable fashion. Working with the Springer publishers, especially Melissa Ramondetta, Executive Editor, Dianne Wuori, Editorial Assistant, and Candace Rosa, Production Editor, was a real pleasure. Their patience, courtesy and efficiency are very much appreciated.