This chapter presents the basic concept for the signal processing techniques to provide tracking of the phases of cardiac motion without electrocardiogram (ECG) gating. This phase information is used to remove the cardiac motion artifacts and reconstruct images with better quality and diagnostic value. These techniques can be implemented on data sets acquired from single and multislice helical computed tomography (CT) scanners. The signal-processing techniques can be used to identify the projection data that corresponds to the "less active" phase of the cardiac cycle. The two proposed signal-processing techniques to identify the less active phase of the cardiac cycle are: the spatial overlap correlator (SOC) with unwrapping filter and a technique based on constant attenuation property of the Radon transform. The purpose of the algorithmic development, detailed in this chapter, was to assess software solutions that can aid in obtaining diagnostic information from such patients where a multislice CT scan can be performed without beta blockade.