A.i) Vortical flow: the IVC and SVC turn in a clockwise vortex. All other flow patterns were classified as non-vortical (abnormal) flow, within this category 3 distinct patterns were identified: ii) Spiral-vortical flow: the IVC forms a vortex whilst the SVC passes laterally and is then enveloped in a spiral fashion by the IVC, iii) Spiral flow: where the IVC and SVC combine in a spiral, iv) Complex flow: involving multiple vortices arising from the IVC and SVC flow. Figure 1B. Right atrial flow patterns in controls compared to patients with a PFO. Figure 1C. Right atrial flow patterns in controls without a PFO, compared to controls with a PFO but no embolic event and patients with a PFO and presumed embolic event.