1. Cardiovascular Magnetic Resonance Unit,
2. Visual Information Processing Group of Department of Computing and
3. Department of Cardiothoracic Surgery, Royal Brompton Hospital site of Imperial College of Science, Medicine and Technology, Sydney Street, London SW3 6NP , UK
4. Flow Design Research Group, Emerson College, Forest Row, East Sussex RH18 5JX, UK

Correspondence to: Philip J. Kilner¹ Correspondence and requests for materials should be addressed to P.J.K. (e-mail: Email: p.kilner@rbh.nthames.nhs.uk).

Through cardiac looping during embryonic development¹, paths of flow through the mature heart have direction changes and asymmetries whose topology and functional significance remain relatively unexplored. Here we show, using magnetic resonance velocity mapping^{2, 3, 4, 5}, the asymmetric redirection of streaming blood in atrial and ventricular cavities of the adult human heart, with sinuous, chirally asymmetric paths of flow through the whole. On the basis of mapped flow fields and drawings that illustrate spatial relations between flow paths, we propose that asymmetries and curvatures of the looped heart have potential fluidic and dynamic advantages. Patterns of atrial filling seem to be asymmetric in a manner that allows the momentum of inflowing streams to be redirected towards atrio-ventricular valves, and the change in direction at ventricular level is such that recoil away from ejected blood is in a direction that can enhance rather than inhibit ventriculo-atrial coupling⁶. Chiral asymmetry might help to minimize dissipative interaction between entering, recirculating and outflowing streams⁷. These factors might combine to allow a reciprocating, sling-like, 'morphodynamic' mode of action to come into effect when heart rate and output increase during exercise⁶.