This paper presents the reactions to Descartes' account of the heartbeat expressed by the Leuven professors Fortunatus Plempius and Libertus Fromondus, reactions that also involved the Utrecht professor Henricus Regius. I show that the letters exchanged between Descartes and the two Leuven professors in 1637–1638 stirred a continuous debate, followed through a series of publications, up to the condemnations of Cartesianism in 1662–1663. I investigate the extent to which the reception of Descartes' account of the heartbeat contributed to the initial rejection of Cartesianism in Leuven and how physiological arguments were motivated by theological concerns throughout these exchanges.