1. Oxford University Computing LaboratoryWolfson Building, Parks Road, Oxford OX1 3QD, UK
2. Cardiac Mechano-Electric Feedback Group, Department of PhysiologyAnatomy and Genetics, Sherrington Building, Parks Road, Oxford OX1 3PT, UK
3. Centre for Mathematical Biology, Mathematical Institute24-29 St Giles', Oxford OX1 3LB, UK