An oven for heating moving thermoplastic blanks (preforms, intermediate containers), which includes conveying devices for supporting and moving the blanks sequentially while rotating each of them about its own axis. A heating device is arranged laterally to the conveying device for heating the moving blank bodies, and the conveying device includes at least two parallel conveying branches, proximate each other and having opposite conveying directions, the two branches being traveled along one after the other by the blanks. The heating device is arranged between the two conveying branches so as to heat simultaneously on both sides of the blanks moving in opposite directions respectively on the two branches.