Cardiac myosin powers the contraction of the heart and has load dependent kinetics that enable it to adjust its power output in response to load. Dysfunction of cardiac myosin's mechanochemistry can lead to diseases including heart failure, and therefore, there is an outstanding need to probe how mutations and potential therapeutic compounds affect myosin's mechanochemistry under load. Given that cardiac myosin has fast cycling kinetics, we have developed a fast optical trapping system specifically tailored towards probing the mechanochemistry of cardiac myosin. A field programmable gate array (FPGA) board digitizes force signals, applies tunable digital filtering for feedback clamping, controls trap positions through fast interfaces to direct digital synthesizer (DDS) boards, and oscillates the sample stage. Amplified frequencies from each DDS drive acousto-optic deflectors for steering the trapping laser beams. This FPGA-DDS feedback system can respond to changes in bead position due to myosin binding in <33 microseconds. The synchronously acquired data include internal trap position commands, calculated feedback errors, and sample stage position. To demonstrate the system capabilities, we examined the mechanochemical properties of cardiac myosin using the three-bead-assay developed by the Spudich lab. Using our system, it is possible to clearly resolve the kinetics and mechanics of the cardiac myosin working stroke. We use an improved methodology for binding event identification and synchronization, enabling better resolution of the substeps of the myosin working stroke. We also demonstrate the ability of this system to probe the load dependent kinetics of cardiac myosin using both an isometric force feedback clamp and harmonic force spectroscopy. The speed of the system enables measurement of these parameters at physiologically relevant ATP concentrations despite the short lived binding interactions between actin and myosin.