1. A system comprising: first and second acoustic transducer interfaces, the first acoustic transducer interface configured to be coupled to a first acoustic transducer located in or about a heart, the second acoustic transducer interface configured to be coupled to a second acoustic transducer; and a controller circuit, coupled to the first and second acoustic transducer interfaces to measure a distance, between the first and second acoustic transducers, that varies during a heart contraction, the controller configured to provide an indication based on a variation of the distance during at least one heart contraction.