Abstract The present study is based on our experience of peripheral arterial embolization in 1,500 consecutive patients with predominant mitral stenosis who underwent mitral valvuloplasty. The purpose of this study has been to define the conditions under which such embolization takes place. It has been shown that the presence of atrial fibrillation, increasing severity of heart disease, and the occurrence of preoperative embolization all increase the risk of operative embolization, which remains an inherent risk of the procedure and is a major factor in deaths from operation. Our findings suggest that an embolus within 8 weeks of operation carries a higher risk of operative embolization than does a preoperative embolus occurring earlier. Our present findings confirm our previous reports with respect to the protective value of mitral valve operation against future embolization. Late postoperative emboli have occurred in 38 patients of the entire group followed up for a mean period of 6 years, an incidence of 0.46 to 0.64 per cent per patient-year. Our figures show no beneficial results from preoperative anticoagulant therapy as given—for most it was given for a short period and stopped several days prior to operation—but shed no light on anticoagulant treatment given intensively for longer periods or through the period of operation. The low incidence of embolization after the immediate operative period would suggest that the routine administration of anticoagulant agents is unnecessary in the postoperative period, either early or late. The formation of peripheral emboli is an indication for mitral valvuloplasty in patients with mitral stenosis, even without symptoms. In certain patients the increased risk of operative embolization is about balanced by the increased hazard of recurrent spontaneous embolization.