The phase, relative to the arterial pressure, of cyclically varying integrated backscatter from canine myocardium was measured at normal and reduced coronary blood flow levels and was found to become more randomized with decreasing flow. The phase, modeled as a von Mises distribution on a unit circle which is very similar to the normal distribution on the line, is characterized by a mean (mu 0) and a concentration or width parameter (kappa). kappa is used to characterize the degree of randomization. The von Mises distribution provides an excellent fit to measured data (p less than 0.01). Hypothesis tests performed on the data for various coronary flow levels indicate that the phase distribution for normal coronary flow level is significantly different from the distributions at other flow levels (p less than 0.05). The results suggest that the parameter kappa may be used for differentiating normal and ischemic myocardium.