Definition: Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.
Input: Abstract: Severe aortic regurgitation developed in three patients after aortic valve replacement within six months due to long sutures prolapsing across the "annulus" of Bjork-Shiley prosthesis. At reoperation the offending sutures were trimmed or tucked back to the aortic wall to eliminate aortic regurgitation. Prolapse of unravelled knots may be the likely cause. Everting the sewing skirt during the first replacement may prevent this complication.

Bjork-Shiley valve malfunction by prolapsed sutures.