This disclosure describes various techniques for discriminating supraventricular tachycardia (SVT) from ventricular tachycardia (VT). As one example, a method includes detecting a tachycardia rhythm, identifying a rate of change in heart rate corresponding to the tachycardia rhythm, identifying a rate of change in heart rate variability corresponding to the tachycardia rhythm, and classifying the tachycardia rhythm as at least one of supraventricular tachycardia or ventricular tachycardia based on the rate of change in heart rate and rate of change in heart rate variability.