We have described a transducer design capable of recording forces generated by single cardiac myocytes with sufficient temporal resolution to detect force responses to rapid length changes. Our force sensors were made from thin steel foils that act as cantilevers whose bending is monitored by reflection off a laser beam. Deflection of the laser beam is measured by a differential photodiode detector. A small, 50-micron-thick tungsten needle attached to the free end of the steel foil allowed us to glue single cardiac cells to the force transducer. The transducers have compliances of approximately 0.02 m/N and resonance frequencies between 2 and 3 kHz. The resolution is approximately 18 nN rms at a detector bandwidth of 16 kHz, so we were able to resolve 0.2% of the maximum isometric force ( approximately 12 microN) developed by a single cardiac myocyte. We have demonstrated that the transducer is well suited to analysis of mechanical properties of single ventricular myocytes, for example, the recording of isometric forces and rate constants of force redevelopment after rapid release-restretch maneuvers.