Atrial myxomas generally do not require urgent surgery. We report on a 78-year-old woman in whom transesophageal echography revealed a large left atrial myxoma. She acutely developed dyspnoea, tachypnoea, and forward failure necessating urgent surgery. The myxoma was surgically removed and showed a haematoma. The most likely reason for the deteriorating condition was acute enlargement of the myxoma due to intramyxomal haemorrhage. This case illustrates that the clinical condition of patients with symptomatic myxoma can deteriorate suddenly and require urgent surgical treatment.