['Mitral ring annuloplasty is routinely applied as an adjunct procedure in reconstructive surgery on the mitral valve leaflets or chordae tendineae. It is assumed that mitral ring annuloplasty relieves tensile stress on the repaired valve tissue and thereby improves the durability of the procedure, but the indication is disputable. We sought to study the effect of mitral ring annuloplasty on the tension of the primary and secondary chordae tendineae of the anterior mitral valve leaflet in vivo.', 'In 17 adult pigs miniature chordal force transducers were sutured to the 2 major fixing primary chordae and the 2 strut secondary chordae of the anterior leaflet. Baseline measurements were accomplished. After randomization, one group (n = 10) underwent a mitral ring annuloplasty (Carpentier-Edwards Classic, 28 mm; Edwards Lifesciences, Irvine, Calif), and the second group (n = 7) served as controls and underwent a sham operation. Simultaneous recordings of chordae tendineae tension and hemodynamics and echocardiographic assessment of anterior leaflet occlusion area were acquired at baseline and after the mitral ring annuloplasty/sham operation.', 'Mitral ring annuloplasty caused a significant reduction of the anterior leaflet occlusion area (1.85 ± 0.16 vs 4.63 ± 0.37 cm(2)) and the tension of the secondary chordae (0.33 ± 0.06 vs 0.67 ± 0.12 N) but did not affect the tension of the primary chordae (0.24 ± 0.07 vs 0.17 ± 0.06 N). The sham procedure had no effect on these variables.'] Does mitral ring annuloplasty relieve tension of the secondary but not primary chordae tendineae in the anterior mitral leaflet?