Fig 1.

Diagram of the syrinx wall and fluid movement during the cardiac cycle. A, The syrinx “at rest” during late diastole with its classic ovoid shape. B, During systole, the superior portion of the syrinx is compressed, forcing a fluid jet caudally, which distends the inferior portion of the syrinx. C, During early diastole, the ballooned inferior portion of the syrinx recoils and forces the fluid rostrally to re-expand the superior portion of the syrinx. Images courtesy of Ms Vicky Earle (vearlemedicalart.com).