The cardiac ventricular myocyte is a key experimental system for exploring the mechanical properties of the diseased and healthy heart. Millions of primary myocytes that remain viable for four to six hours can be readily isolated from animal models. However, the mechanical properties of only a few physically loaded myocytes can be explored in this time using current instrumentation. Here we describe a prototype instrument that is both modular and inexpensive and could form the basis of an array of devices for probing the mechanical properties of single mammalian myocytes in parallel. This would greatly increase the throughput of scientific experimentation and could be applied as a high content screening instrument in the pharmaceutical industry. The instrument module consists of two independently controlled Lorentz force actuators / force transducers in the form of stainless steel cantilevers with dimensions 0.025 mm x 1 mm x 5 mm, 0.5 m/N compliance and 360 Hz resonant frequency. Optical position sensors focused on each cantilever provide position and force resolution < 1 nm/Hz and < 2 nN/Hz respectively. The motor structure can produce peak displacements and forces of ± 200 µm and ± 400 µN respectively. Custom Visual Basic.Net software provides data acquisition, signal processing and digital control of cantilever position. The functionality of the instrument was demonstrated by implementing novel methodologies for loading and attaching healthy, mammalian ventricular myocytes to the force sensor and actuator and measuring their passive dynamic stiffness at varied sarcomere lengths using stochastic system identification techniques.