A medical device for delivering therapy in response to a cardiac event, comprising: a housing; sensing circuitry (190, 178, 142, 144) positioned within the housing and configured to obtain a cardiac signal sensed via a plurality of electrodes (18, 20, 22) electrically coupled to the sensing circuitry, the plurality of electrodes forming a first sensing vector and a second sensing vector; and said sensing circuitry further configured to analyze the sensed cardiac signal to identify the cardiac event as one of a shockable event or a non-shockable event based on a first segment of the cardiac signal sensed along the first sensing vector during a first predetermined sensing window and a second segment of the cardiac signal simultaneously sensed along the second sensing vector during the predetermined sensing window, and characterized by said sensing circuitry being further configured to determine, in response to the cardiac event being identified as a shockable event, a first R-wave morphology corresponding to R-waves of a third segment of the cardiac signal subsequently sensed along the first sensing vector during a second predetermined sensing window and a second R-wave morphology corresponding to R-waves of a fourth segment of the cardiac signal subsequently sensed along the second sensing vector during the second predetermined sensing window, determine whether the third segment of the cardiac signal and fourth segment of the cardiac signal satisfy a monomorphic signal metric, and identify the cardiac event as one of a monomorphic ventricular tachycardia or a polymorphic ventricular tachycardia based on the determined first R-wave morphology, second R-wave morphology, and the third and fourth segments of the cardiac signal satisfying the monomorphic signal metric. a housing; sensing circuitry (190, 178, 142, 144) positioned within the housing and configured to obtain a cardiac signal sensed via a plurality of electrodes (18, 20, 22) electrically coupled to the sensing circuitry, the plurality of electrodes forming a first sensing vector and a second sensing vector; and said sensing circuitry further configured to analyze the sensed cardiac signal to identify the cardiac event as one of a shockable event or a non-shockable event based on a first segment of the cardiac signal sensed along the first sensing vector during a first predetermined sensing window and a second segment of the cardiac signal simultaneously sensed along the second sensing vector during the predetermined sensing window, and characterized by said sensing circuitry being further configured to determine, in response to the cardiac event being identified as a shockable event, a first R-wave morphology corresponding to R-waves of a third segment of the cardiac signal subsequently sensed along the first sensing vector during a second predetermined sensing window and a second R-wave morphology corresponding to R-waves of a fourth segment of the cardiac signal subsequently sensed along the second sensing vector during the second predetermined sensing window, determine whether the third segment of the cardiac signal and fourth segment of the cardiac signal satisfy a monomorphic signal metric, and identify the cardiac event as one of a monomorphic ventricular tachycardia or a polymorphic ventricular tachycardia based on the determined first R-wave morphology, second R-wave morphology, and the third and fourth segments of the cardiac signal satisfying the monomorphic signal metric.