The invention relates to a heat engine (29), including a drive unit (1) provided with: a casing (2) delimiting therein an annular chamber (12), two triads of pistons (7a-7b-7c; 9a-9b-9c) rotatably housed in the casing of the annular cylinder (or toroidal cylinder), a three-shaft movement system (18) configured to transmit motion from and/or to the two triads of pistons; wherein the heat engine is configured so as to carry out a Rankine or Rankine-Hirn thermodynamic cycle, capable of producing electrical energy and heat; the same invention further relates to a pneumatic motor (61) including the aforesaid drive unit (1), configured so as to transform the compressed air at high pressure, contained in a tank, into mechanical energy.