Phase Singularity Dynamics Introduction: Quantitative analysis of complex self-excitatory wave patterns, such as cardiac ” brillation and other high-order reentry, requires the development of new tools for identifying and tracking the most important features of the activation, such as phase singularities. Methods and Results: Image processing operations can be used to detect the phase singularity at the tip of a spiral wave. The phase space behavior of a spatiotemporal sequence of data may be reconstructed using time-series analysis. The phase singularities then are localized ef” ciently by computing the topologic charge density as the curl of the spatial phase gradient. We analyzed the singularity interaction dynamics of both experimentally observed and numerically simulated instances of quatrefoil reentry and found that the singularity behavior in the experimental preparations can be classi” ed into three categories on the basis of how their separation changes with time. Conclusion: Topologic charge densities can be calculated easily and ef” ciently to reveal phase singu-larity behavior. However, the differences between theoretical and experimental observations of singularity separation distances indicate the need for more sophisticated numerical models. © 2001 Futura Publishing Company, Inc.