The article is dedicated to an interpretation of one of the texts forming what James I. Wimsatt has called «the Marguerite poetry of Guillaume de Machaut». Its aim is to show that the French poet, in the verses of Mon cuer, m’amour, ma dame souverainne, not only exploited the meaning of the Latin noun margarita, ‘pearl’, in order to make use of it in the praise of a lady bearing that name, but also seems to have taken account of a patristic tradition that assimilates the margarita mentioned in a parable of the Gospel of St Matthew to the sweetness of celestial life. The hypothesis that Machaut, a canon of Reims cathedral, had this allegorical interpretati on in mind when conceiving his poem, offers an explanation of the insistence on the lady’s unique sweetness in several passages of the poem, especially in its conclusion. Besides this, the article illustrates Machaut’s brilliance in the employ of a rhetorical artifice that sets Mon cuer, m’amour, ma dame souverainne, apart from the rest of his poetic production: the acrostic.