Differences of the effect of annuloplasty rings on the mitral annulus and leaflets, and differences between types of annuloplasty rings are not well known. We analyzed annular motion and leaflet movement with a rigid or flexible ring and without a ring using an isolated swine working heart model. Hearts of 10 swine (weight: 40-50 kg) were used for a rigid ring (n=5) and a flexible ring (n=5). Four ultrasound crystal tips were fixed around the annulus and an annuloplasty ring was implanted in the isolated heart. In the working heart mode, measurement of mitral annular dimension was acquired by sonomicrometry. Images of mitral valve motion were acquired by a high-speed video camera. The same analyses were performed after removing the artificial ring. The antero-posterior diameter of the diastole distance was significantly reduced in the flexible ring (21.59±0.71 mm) and rigid ring (15.93±1.88 mm) compared with no ring (23.51±2.01 mm). The flexible ring made the transverse diameter shrink significantly more than did the rigid ring. The contraction range of the transverse diameter was significantly smaller in the flexible ring compared with no ring. The duration of opening to closing of the mitral leaflet with the rigid (124.7±4.4 ms) and flexible rings (107.9±3.5 ms) was significantly shorter than that with no ring (168±36.5 ms). Annuloplasty rings allow simplicity of leaflet motion, regardless of the type of artificial ring. In a flexible ring, the mitral annulus shows a vertically long shape, suggesting preservation of posterior annular movement.