The MICROCARD project will develop an exascale simulation platform to study the mechanisms of cardiac arrhythmia with mod-els that represent the heart cell by cell. 

Cardiac arrhythmia, which are among the most frequent causes of death, are disorders of the electrical synchronization system of the heart. Numerical models of this complex system are already highly sophisticated and widely used, but to match observations in aging and diseased hearts they need to move from a continuum approach to a representation of individual cells and their interconnections. This implies a different, harder numerical problem and a 10,000-fold increase in problem size, and consequently a transition from tier 1 to exascale systems. Moreover, the project aims to limit its climate impact by developing energy-efficient code, and operates in a domain where numerical simulation is all but commonplace. 

To meet these challenges the platform is co-designed by HPC experts, numerical scientists, biomedical engineers, and biomedical scientists, from academia and industry. We develop numerical schemes suitable for exascale parallelism together with matching linear-system solvers and preconditioners, and a dedicated compiler to translate high-level model descriptions into optimized, energy-efficient system code for heterogeneous computing systems. The code will be resilient to hardware failures and will use an energy-aware task placement strategy. 

At the same time, we develop highly parallel mesh generation software to build the extremely large and complex models that we will need for our simulations. These meshes will be based on large volumes of confocal microscopy data that were recently acquired with the latest clearing and labelling techniques. 

Our simulation platform will be applied to real-life use cases and will be made accessible for a wide range of users. It will be adaptable to similar biological systems such as nerves, and some of the components and techniques will be reusable in a wide range of applications. 

MICROCARD is coordinated by the IHU Liryc, an institute dedicated to research on cardiac arrhythmia that is part of the University of Bordeaux (France) and its university hospital. The project also has strong ties with the Institute for Experimental Cardiovascular Medicine in Freiburg (Germany), and several other clinical and experimental research groups. Together with an end-user advisory board composed of prominent experimental and clinical cardiologists these links will help us to have a real impact on cardiology research and ultimately on patient care.