A retrospective analysis of intramyocardial coronary arterial changes was done in excised papillary muscles obtained at surgery in 46 cases with rheumatic mitral valve disease (RMVD). The findings were correlated with left ventricular function. Vessel wall thickening with obliteration of the lumen was found in 15 patients (32.6%) while adventitial and peri vascular fibrosis was found in 12 cases (26 %). Patients with microarteriopathy had significantly higher left ventricular and diastolic pressure (p < 0.05), lower ejection fraction (p < 0.001), and lower cardiac index (p < 0.01), as compared to patients with no microarteriopathy. The incidence of left ventricular dysfunction and surgical mortality was higher in patients with microarteriopathy (80 and 47%, respectively) than in those with normal microvasculature (26 and 13 %, respectively). As a test for predicting left ventricular dysfunction and surgical mortality a positive biopsy was moderately sensitive (sensitivity 60 and 64%, respectively) and highly specific (specificity 88 and 77%, respectively). Successful outcome after mitral valve replacement was correctly predicted by a negative biopsy result in 87% cases. We conclude that in RMVD, microarteriopathy is associated with left ventricular dysfunction and poor postoperative prognosis.