This report describes six previously healthy infants with acute mitral valve chordal rupture. Although their initial symptoms were mild respiratory distress and fever, all the infants presented with acute progressive left heart failure and required urgent surgical repair. Mitral valve annuloplasty and mitral valve replacement were performed (for three patients each). Two patients died, both of whom had cardiac arrest and required resuscitation before surgery. Histologic examination of excised mitral valve leaflets showed infiltration of gram-positive bacteria in these two patients. All the patients were 4-6 months old, which may suggest underlying congenital factors. The authors believe early diagnosis and surgery are crucial as a life-saving measure for infants with acute mitral valve chordal rupture.