A medical device, comprising: a sensing module coupled to a plurality of electrodes (24, 28, 30) defining a plurality of available sensing vectors, the sensing module receiving the cardiac signals using selected ones of the plurality of available sensing vectors; and a control module coupled to the sensing module and configured to: sense a first cardiac signal during a known cardiac rhythm from each of the plurality of available sensing vectors; for each of the plurality of available sensing vectors, generate a plurality of morphology templates of the first cardiac signal for each of a plurality of patient postures; determine a set of template features from each of the plurality of morphology templates; for each of the plurality of available sensing vectors, compare the set of template features from one of the plurality of morphology templates corresponding to one of the plurality of postures to each of the sets of template features from all of the other morphology templates corresponding to all of the other of the plurality of postures; for each of the plurality of available sensing vectors, store a set of posture-independent template features in response to the comparing; sense a second cardiac signal during an unknown cardiac rhythm from at least one of the plurality of available sensing vectors; determine features from the second cardiac signal that are analogous to the set of posture-independent template features stored for the at least one of the plurality of available sensing vectors; compare the features determined from the second cardiac signal to the analogous set of posture-independent template features; and classify the unknown cardiac rhythm as treatable or non-treatable in response to comparing the features determined from the second cardiac signal to the analogous set of posture-independent template features. a sensing module coupled to a plurality of electrodes (24, 28, 30) defining a plurality of available sensing vectors, the sensing module receiving the cardiac signals using selected ones of the plurality of available sensing vectors; and a control module coupled to the sensing module and configured to: sense a first cardiac signal during a known cardiac rhythm from each of the plurality of available sensing vectors; for each of the plurality of available sensing vectors, generate a plurality of morphology templates of the first cardiac signal for each of a plurality of patient postures; determine a set of template features from each of the plurality of morphology templates; for each of the plurality of available sensing vectors, compare the set of template features from one of the plurality of morphology templates corresponding to one of the plurality of postures to each of the sets of template features from all of the other morphology templates corresponding to all of the other of the plurality of postures; for each of the plurality of available sensing vectors, store a set of posture-independent template features in response to the comparing; sense a second cardiac signal during an unknown cardiac rhythm from at least one of the plurality of available sensing vectors; determine features from the second cardiac signal that are analogous to the set of posture-independent template features stored for the at least one of the plurality of available sensing vectors; compare the features determined from the second cardiac signal to the analogous set of posture-independent template features; and classify the unknown cardiac rhythm as treatable or non-treatable in response to comparing the features sense a first cardiac signal during a known cardiac rhythm from each of the plurality of available sensing vectors; for each of the plurality of available sensing vectors, generate a plurality of morphology templates of the first cardiac signal for each of a plurality of patient postures; determine a set of template features from each of the plurality of morphology templates; for each of the plurality of available sensing vectors, compare the set of template features from one of the plurality of morphology templates corresponding to one of the plurality of postures to each of the sets of template features from all of the other morphology templates corresponding to all of the other of the plurality of postures; for each of the plurality of available sensing vectors, store a set of posture-independent template features in response to the comparing; sense a second cardiac signal during an unknown cardiac rhythm from at least one of the plurality of available sensing vectors; determine features from the second cardiac signal that are analogous to the set of posture-independent template features stored for the at least one of the plurality of available sensing vectors; compare the features determined from the second cardiac signal to the analogous set of posture-independent template features; and classify the unknown cardiac rhythm as treatable or non-treatable in response to comparing the features determined from the second cardiac signal to the analogous set of posture-independent template features.