1. A system, comprising: a sensing input configured to sense a tachyarrhythmia; a rhythm sensor, coupled to the sensing input, configured to: compare a sensed tachyarrhythmia with a ventricular tachyarrhythmia criterion; and compare a sustained tachyarrhythmia with a supraventricular tachyarrhythmia (SVT) criterion in response to the tachyarrhythmia continuing during or after a diagnostic neural stimulation; a neural stimulation generator, coupled to the rhythm sensor, configured to provide the diagnostic neural stimulation in response to a determination that the sensed tachyarrhythmia does not satisfy the ventricular tachyarrhythmia criterion; and a ventricular tachyarrhythmia therapy generator, coupled to the rhythm sensor, configured to: provide a ventricular tachyarrhythmia therapy in response to a determination that the sensed tachyarrhythmia satisfies the ventricular tachyarrhythmia criterion; and provide a ventricular tachyarrhythmia therapy in response to a determination that the sensed tachyarrhythmia does not satisfy the SVT criterion.