An intracardiac pacemaker comprising: a housing sized to fit within a heart; at least two electrodes (162, 164) disposed on the housing; a sensing module enclosed within the housing and electrically coupled to the at least two electrodes, the sensing module configured to sense R-waves from a first cardiac electrical signal received from the at least two electrodes coupled to the sensing module; a pulse generator enclosed within the housing and electrically coupled to the at least two electrodes, the pulse generator configured to generate cardiac pacing pulses for delivery to the heart via the at least two electrodes; and a control module enclosed within the housing and electrically coupled to the sensing module and the pulse generator, the control module configured to: determine RR intervals between consecutive ones of the sensed R-waves; apply RR interval-based ventricular tachycardia detection criteria solely to the determined RR intervals; detect a monomorphic VT when the VT detection criteria are met; and control the pulse generator to deliver anti-tachycardia pacing in response to detecting the monomorphic VT, wherein applying the detection criteria solely to the determined RR intervals comprises applying at least a non-sinus rhythm criterion, a supraventricular tachycardia rejection criterion, and a criterion of a threshold number of tachycardia detection intervals to the RR intervals. a housing sized to fit within a heart; at least two electrodes (162, 164) disposed on the housing; a sensing module enclosed within the housing and electrically coupled to the at least two electrodes, the sensing module configured to sense R-waves from a first cardiac electrical signal received from the at least two electrodes coupled to the sensing module; a pulse generator enclosed within the housing and electrically coupled to the at least two electrodes, the pulse generator configured to generate cardiac pacing pulses for delivery to the heart via the at least two electrodes; and a control module enclosed within the housing and electrically coupled to the sensing module and the pulse generator, the control module configured to: determine RR intervals between consecutive ones of the sensed R-waves; apply RR interval-based ventricular tachycardia detection criteria solely to the determined RR intervals; detect a monomorphic VT when the VT detection criteria are met; and control the pulse generator to deliver anti-tachycardia pacing in response to detecting the monomorphic VT, wherein applying the detection criteria solely to the determined RR intervals comprises applying at least a non-sinus rhythm criterion, a supraventricular tachycardia rejection criterion, and a criterion of a threshold number of tachycardia detection intervals to the RR intervals. determine RR intervals between consecutive ones of the sensed R-waves; apply RR interval-based ventricular tachycardia detection criteria solely to the determined RR intervals; detect a monomorphic VT when the VT detection criteria are met; and control the pulse generator to deliver anti-tachycardia pacing in response to detecting the monomorphic VT, wherein applying the detection criteria solely to the determined RR intervals comprises applying at least a non-sinus rhythm criterion, a supraventricular tachycardia rejection criterion, and a criterion of a threshold number of tachycardia detection intervals to the RR intervals.