Oh, I remember how difficult it was to design this pattern! (First posted 4 July 2015.) Designing is a lot easier now.
Sunken Heart
Row 1: Plain weave (P)
Row 2: (U3, O1) x 7, U3
Row 3: P2, (U3, O1) x 2, U3, P5, (U3, O1) x 2, U3, P2
Row 4: (U3, O1) x 2, U3, P9, (U3, O1) x 2, U3
Row 5: P2, U3, O1, U3, P13, U3, O1, U3, P2
Row 6: U3, O1, U3, P17, U3, O1, U3
Row 7: P2, U3, P21, U3, P2
Row 8: U3, P25, U3
Row 9: P
Row 10: Repeat row 8
Row 11: P
Row 12: Repeat row 8
Row 13: P2, (U3, P9) x 2, U3, P2
Row 14: (U3, O1, U3, P5) x 2, U3, O1, U3
Row 15: P2, (U3, O1) x 6, U3, P2
Row 16: P
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Sunken Heart—mini, version 1
Sunken Heart—mini, version 1
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Sunken Heart—mini, version 2
Sunken Heart—mini, version 2