We have used the solar wind electron heat flux flow directions to determine the interplanetary magnetic field polarities for the ISEE 3 period from 1978 to 1982. This technique assumes that the heat flux electrons flow away from the Sun along magnetic field lines. It provides the field polarities independently of the field directions. The resulting distribution of sector durations and the changes in that distribution with solar activity cycle are presented for four 1-year periods. The large-scale sectors expected from extrapolation of the Stanford source surface maps are present along with a population of small-scale sectors with a peak in the time range of 9 hour to 1 day. About half the small-scale sectors contain bidirectional electron (BDE) flows, suggesting their origins in coronal mass ejections. We also examine cases of false polarities, in which the directions of the fields imply polarities opposite to those determined from the heat-flux directions. These constitute only 6 to 8% of all the hourly averages of the data. The majority (78%) of these false polarity regions were not associated with BDEs, and 75% were of only 1 or 2 hour durations. False polarity regions tended to lie nearly orthogonal to the spiral field angles and at relatively high latitudinal angles. While multiple (≥3 in 24 hours) current sheet crossings are common, we find no cases consistent with a wavy current sheet. ¿ 1998 American Geophysical Union