With cardiac resynchronization treatment, a device is implanted in the chest to help the heart's segments squeeze (contract) more systematically and effectively. The majority of heart failure (HF) devices in diagnostic use or actively being researched fall into one of four categories: those that screen the HF condition, those that treat rhythm problems, those that increase the mechanical characteristics of the heart, and those that replace all or part of the heart's functions. However, in contemporary clinical practice, devices that deliver cardiac resynchronization treatment (CRT) or prevent sudden cardiac death (SCD) by quickly resolving ventricular tachycardia (VT) or fibrillation are the most often used uses of device therapy in heart failure.