Myosins are a family of motor proteins responsible for various forms of cellular motility, including muscle contraction and vesicular transport. The most fundamental aspect of myosin is its ability to transduce the chemical energy from the hydrolysis of ATP into mechanical work, in the form of force and motion. A key unanswered question of the transduction process is, "what is the relative timing between the powerstroke and release of phosphate Pi from the active site?". We examined the ability of single-headed myosin Va to generate a powerstroke in a single molecule laser trap assay while maintaining Pi in its active site in of of two ways: 1) by elevating Pi in solution or 2) by introducing a mutation in myosin's active site (S217A) which slow Pi-release from the active site. An autaomted analysis program for the detection of single molecule binding events was developed and showed that upon binding to the actin filament, WT myosin generated a powerstoke rapidly (500/s) and without a detectable delay, both in the absence and presence of 30 mM Pi . The elevated levels of Pi did, however, affect event lifetime, eliminating the longest 25 percent of binding events, confirming that Pi rebound to myosin's active site and accelerated detachment. The S217A construct also generated a powerstroke similar in size and rate upon binding to actin despite the slower Pi release rate. These findings provide direct evidence that myosin Va generates a powerstroke with Pi still in the active site. Therefore, the findings are most consistent with a model in which the powerstroke occurs prior to the release of Pi from the active site.