The aim of this paper is to discuss the themes of objectivity and neutrality as present in scientific movies of medical content produced by Brazilian documentarist Benedito Junqueira Duarte. The production of images of a specific practice – the first experimental surgeries for implantation of cardiac valves and pace-makers – carried on during the early 1960s, were used for the presentation of new medical instruments, materials, equipments and procedures related to the field of heart surgery and transplantation. In this process, the representation of instruments and materials helped to build a language characteristic of the film-maker's production, and at the same time promoted the construction of a given scientific memory, associated with certain institutions and characters of Brazilian medicine. As pointed out by Bruno Latour and Karin Knorr-Cetina, it is interesting to evaluate the observation of nature as an activity mediated by several elements that "fixate" a given relation, which, after a long process of "translation", may circulate freely and solidify as a verifiable, consistent fact. When its path is traced out, this circulation reveals itself to be based upon canons in which the relations of truth, objectivity and neutrality are the results, and not the starting-points, of scientific practice. Two movies of Benedito Junqueira Duarte are highlited here: "Marca-passo implantável" and "Válvula Cardíaca", both from 1968, produced under the scientific consultancy of cardiac surgeon Adib Jatene (regarded today by the Brazilian public as a pioneer developer of heart-surgery instruments). Starting from these movies I intend to discuss some points related to the notions of "being true to the facts and phenomena of science", and the presence of cinematic language as the locus of action of a scientific discourse based on technological apparatus, instruments and experimentation. In this case, such relations conferred to what is specifically cinematic the function of producing truth-proofs about the "natural" world, here represented by the human body.