Cardiac monitoring and/or stimulation methods and systems that provide one or more of monitoring, diagnosing, defibrillation, and pacing. Cardiac signal separation is employed to detect, monitor, track and/or trend a patient's posture using cardiac activation sequence information. Devices and methods involve sensing a plurality of composite cardiac signals using a plurality of implantable electrodes. A source separation is performed using the composite cardiac signals, which produces one or more cardiac signal vectors associated with all or a portion of one or more cardiac activation sequences. A change in a patient's posture is detected using the cardiac signal vectors. Further embodiments involve sensing the plurality of composite cardiac signals during the patient's predominant cardiac rhythm before detecting the change in the patient's posture. Other embodiments involve discriminating between one of a postural related change and a cardiac rhythm related change using the cardiac signal vectors.