Cold, flowing hydrogen and helium ions are observed with the retarding ion mass spectrometer on Dynamics Explorer 1 in the dayside magnetosphere at subauroral latitudes at 4500-km altitude. These ions show a marked flux asymmetry with respect to the relative wind direction. The observed data can be effectively modeled as drifting Maxwellian distributions perturbed by a first-order Spitzer-H¿rm heat flux distribution function. At high values of L,~14, both species are supersonic, and the shape and direction of the asymmetry are consistent with the presence of an upward heat flux. As L decreases to ~6, both species evolve smoothly into warmer, subsonic upward flows with downward heat fluxes. In the subsonic cases this implies a significant heat source at higher altitudes. These results are found to match theoretical predictions for the polar wind. However, in both cases, in order to match the observed departures from a simple drifting Maxwellian, the mean free path must be as much as one-half the thermal gradient scale length. This strongly suggests that collisionless effects are stronger than predicted and dominate the heat transport throughout the entire transition from supersonic to subsonic flow. These observations demonstrate a capability to observe transport effects in plasmas as higher moments of the distribution function, making possible comparisons with hydrodynamic theories which have until now been experimentally unverified.