Cardiac leiomyosarcoma is a rare tumour which can grow either intramurally or extramurally. Its prognosis is dismal. Surgery lengthens survival, but recurrences usually occur in the short term. Gated MRI is useful for the assessment of cardiac masses since it provides fine spatial and contrast resolution. We present the case of a left atrial leiomyosarcoma whose recurrence was diagnosed by gated MRI. Our patient underwent a second resection but died soon after.