Objectives: to report the case of a patient with a monochorionic-biamniotic twin gestation complicated by TRAP sequence that gave rise to the birth of a pump fetus without anatomical malformations (1932 g) and an acardiac anceps fetus (1800 g), and to review this pathology and the importance of its early diagnosis and management. Materials and methods: the case of an acardiac fetus is presented in a pregnant woman without strict control at the Hospital San Pedro de Logroño in 2019, worthwhile because of its late diagnosis and high birth weight. A search of the literature was carried out in the Medline databases via PubMed, OVID, Embase and SciELO with the MeSH terms. As inclusion criteria, we considered series-type articles and case reports, cohorts and review articles from January 1950 to January 2020. Results: 39 bibliographic references were included with the main theoretical questions to be reviewed. Our acardiac fetus weight was very high comparing with the bibiography and without causing repercussion in the healthy fetus, which contributes to the uniqueness of the case, only the series report by Brassard et al ( 1999) is comparable, with weights of the acardiac fetus above 1700 grams and differing by 100 grams from the pump fetus. Conclusions: the acardiac fetus is an infrequent complication of monochorionic twin pregnancies. The presence of placental vascular anastomoses between both circulations is required. Early diagnosis is important to decrease morbidity and to use, as far as possible, non-invasive therapeutic techniques.