Background The late hemodynamic effects of preserving the papillary muscles during mitral valve replacement have not been evaluated.Methods and Results Sixteen patients who had chronic mitral regurgitation due to myxomatous degeneration were randomized to preservation (Pres group, n=8) or no preservation (No Pres group, n=8) of the chordae tendineae and papillary muscles during mitral valve replacement.Rest and exercise nuclear ventriculograms were performed early (3 months) and late (5 years) after surgery. Early after surgery, the No Pres group had lower ejection fractions and stroke work indexes (P<.05 by repeated-measures (rm) ANOVA) than the Pres group did at similar end-diastolic volume indexes. The No Pres group had similar cardiac indexes after exercise because heart rate increased (P<.005 by rm ANOVA). Late after surgery, ejection fraction was greater at similar end-diastolic volume indexes (P<.005 by rm ANCOVA), and preload recruitable stroke work indexes (P<.001 by rm ANCOVA) were better in the Pres group.Conclusions Preserving chordal attachments enhanced the late hemodynamic recovery after mitral valve replacement for mitral regurgitation.(Circulation. 1994;90(part 2):II-190-II-194.)