An IMD can be implanted into a patient to address various conditions. The IMD case and leads can have various electrodes and other portions to measure various physiological conditions. For example, a selected current can be generated between two electrodes, either external or internal in the patient, and a voltage can be measured by one or more electrodes of the IMD. A voltage can be measured at two or more locations to determine a relative motion of different electrodes. If the electrodes are in different portions of the heart, a determination can be made of a relative motion or position of the heart or portions of the heart.