A work-loop calorimeter for measuring the force-length-heat relationship of working excised cardiac muscle fibers.

Isolated cardiac trabeculae are convenient specimens with which to study the properties of cardiac muscle under a variety of controlled conditions in vitro. We have developed an instrument for measuring the mechanical and energetic properties of continuously-superfused cardiac trabeculae. Our instrument is capable of dynamically transitioning between fixed-length, isometric and isotonic modes of control during the time-course of a muscle twitch, allowing us to impart force-length work-loops that mimic the behaviour of cardiac muscle in vivo. Simultaneously, sensitive temperature transducers quantify muscle heat production. The combination of these interventions and measurements yields unique insight into the energetic efficiency of living cardiac muscle.