Lutgardis was a Flemish-speaking girl who entered the Benedictine convent of St. Catherine of Sint-Truiden at twelve and the Cistercian abbey of Aywières (then in Walloon-speaking territory) at twenty-four — a deliberate transfer she undertook to escape becoming an abbess and to embrace a stricter observance. She lived at Aywières for forty years, never learning more than a few words of French and remaining throughout an exile in language as in life.
Her mystical life, recorded by her contemporary biographer Thomas of Cantimpré who knew her well, was extraordinarily early and graphically Christocentric: visions of Christ exchanging his heart for hers (one of the earliest documented Sacred Heart experiences in Christian mysticism, three centuries before the Visitation revelations to Margaret Mary Alacoque), of his side-wound, and of him asking her to take on penance for sinners.
She undertook three seven-year fasts — most famously the seven years on bread and water in atonement for the Albigensian heresy. She went blind eleven years before her death, which she experienced not as deprivation but as one further immersion in the Passion. Her cult, strong in Belgium and the Cistercian world, was central to the development of Sacred Heart devotion through the late medieval Flemish mystical tradition.