Cardiac volume sensing via an implantable medical device in support of cardiac resynchronization therapy

A leadless cardiac pacemaker (LCP) configured to be implantable in a ventricle of a patient's heart, the LCP comprising:

• a housing comprising rigid body and a tail;
• a first electrode secured relative to the rigid body and exposed to the environment outside of the housing;
• a second electrode secured relative to the tail and exposed to the environment outside of the tail, the second electrode is spaced from the first electrode;
• and
• circuitry in the housing operatively coupled to the first electrode and the second electrode, the circuitry configured to identify a measure of impedance between the first electrode and the second electrode at each of a plurality of times during a cardiac cycle, wherein each measure of impedance represents a measure of volume of the ventricle in which the LCP is implanted;
• and
• the circuitry may be configured to store the measure of impedance between the first electrode and the second electrode at each of a plurality of times during a cardiac cycle in a memory.