Atrial fibrillation is one of the most prolific heart conditions in the UK and, while not usually fatal by itself, it typically leads to other more serious complications such as strokes. In a healthy heart, an electrical impulse is produced periodically at the sinoatrial node and propagates steadily through the atrial tissue resulting in a regular coordinated muscle contraction. Damage to the atrial myocardium alters its conduction and restitution properties which may lead to the creation of complex patterns known as arrhythmias. These make the atrial muscles quiver instead of fully contracting.

The mono-domain model is a reaction-diffusion equation which mimics the electro-physiological activity of cardiac cells. It is a homogenised form of the bidomain model which reduces the large number of ordinary differential equations used to represent each ion channel into just two partial differential equations. This allows for the simulation of electrical conduction on a complete atrial geometry using modest computing resources. The mono-domain model is of the form

where is the transmembrane potential and is the recovery variable. The reaction terms, and , represent the cumulative behaviour of the cell ion channels. The choice of these terms gives rise to several forms:

This model was originally developed to model squid nerve axons:

The original FHN model was modified to produce action potentials which more quantitatively match those seen in myocardium: