A 71-year-old woman presented to the emergency department because of sudden fatigue and shortness of breath. On examination, her pulse rate was 127 beats/min, respiratory rate 28 breaths/min, and oxygen saturation level 91% on ambient air. On auscultation, she had a late diastolic "plop" in the mitral valve area. Her electrocardiogram was normal, and the brain natriuretic peptide level was >5000 pg/mL. Transesophageal echocardiogram demonstrated a 75 Â 45-mm left atrial lesion causing mitral valve obstruction (Figure 1, asterisk; Videos 1 to 4).