The annular annuloplasty was sized to obtain a mild to moderate downsizing of the aortic annulus diameter of 10–15% in systole, which corresponded to a 22-mm Dacron ring [15], and a 20-mm Dacron ring at the STJ was used to complete the double-ring procedure. A standardized approach was used for the 2 annuloplasty procedures (Fig. 1C and D). For the single-ring procedure, an open ring of Dacron tube graft with a height of 4 mm and a diameter of 22 mm was used. The Dacron ring was anchored with 6 U-stitches around the aortic annulus to fasten the ring in the subvalvular position as described by Lansac et al. [19]. Due to the close proximity of the left coronary artery to the myocardium in the pig, it was not possible to position the ring under the left main coronary artery. The ring was opened and anchored closely at each side of the left coronary artery with U-stitches. For the double-ring procedure, we used an additional Dacron ring at the STJ, with a height of 4 mm and a diameter of 20 mm [3]. The Dacron ring was secured with 3 U-stitches above each sinus, and was closed by one of the anchoring U-sutures, to ensure that the ring was circumferential. The aorta was closed using running 4–0 Prolene® sutures. Mikro-Tip pressure catheters (SPR-350, Millar Instruments, Houston, TX, USA) were placed in the left ventricle through the apex and the ascending aorta through the aortotomy. After reperfusion, weaning off ECC and haemodynamic stabilization, data collection was performed for 20 s, with the acquisition of simultaneous pressure, force and electrocardiogram (ECG) data for both groups. Hereafter, the force transducers were released and removed to acquire simultaneous pressure, geometrical and ECG data without influence from the transducers for both groups. See the flowchart of the experimental protocol in Fig. 3. Two-dimensional echocardiography (Vivid I, GE Vingmed Ultrasound AS, Horten, Norway) was performed to verify valve competence at baseline, and after single- and double-ring implantation. The animals were euthanized with an overdose of pentobarbital. The heart was excised and the position of the sonomicrometry crystals and annuloplasties were verified. All animals were operated under standardized conditions by the same surgeon.