Poitrenaud, the only recognised number 15 in the Les Bleus squad, was expected to start against the Pumas, but Heymans' strong showing in the position in the 34-7 warm-up win over Wales eight days ago has swayed the selectors' thinking.
David Skrela and Pierre Mignoni have been named as the half-backs, meaning Toulouse pair Jean-Baptiste Elissalde and Frederic Michalak have to be content with places on the bench.
As expected, powerful Clermont-Auvergne star Aurelien Rougerie beats Vincent Clerc to a place on the wing.
In the fiercely contested back-row department, Remy Martin gets the nod at flanker while Imanol Harinordoquy is selected at number eight ahead of Julien Bonnaire, who is on the bench.
Five of the seven substitutes named by the French are forwards, with Les Bleus clearly expecting a tough battle up front against Argentina.