This paper presents a stability analysis of ventricular tachycardia (VT). Cardiac electrical activity in 5 sheep with induced myocardial infarction was monitored with endocardial electrodes and on the body surface during and following induction into tachycardia. Consecutive cycle times were used to create a discrete state variable vector. Data were then classified into one of four categories - induction, steady-state tachycardia, termination into sinus rhythm, or termination into fibrillation. A discrete `map' or predictive equation was then fitted to data from each of these periods of behavior. An eigen-analysis was performed to determine stability. Mean squared error for the map was also calculated, as an indicator of the quality of the fit. The MSE also indicates the degree of determinism. Preliminary results indicate that this method may be useful in quantifying the stability of cardiac rhythms.