A unitary flexible sheet is folded to defines a panel, and first and second tabs. Each of the tabs has an inner layer and an outer layer. First and second prosthetic leaflets are coupled to a tubular frame via the sheet. Each of the leaflets has a respective commissural portion. For each of the commissural portions, a first region of the commissural portion is sandwiched between inner layers of the first and second tabs, and a second region of the commissural portion is disposed flat against the panel. Other embodiments are also described.