Ten years ago, no one would have listened. As more doctors and researchers begin to pay attention, the virtual heart should increasingly replace real hearts in research. But if the real power of the model lies in gauging the performance of the whole organ, the secret to its success lies at a lower level. Heart muscle cells are wonders of complexity, and capturing the essence of that complexity in mathematics is Noble's forte. Long and thin, each cell contains fibre-like proteins capable of contracting, and a membrane to separate the cell from the outside.
Proteins embedded in the membrane carry crucial signals or materials from one side to the other.
Tiny pumps, for example, push positive and negative ions across the membrane and maintain different concentrations of ions inside and outside the cell. Other proteins in the membrane, called ion channels, act as floodgates. When they open, ions rush through. Inside, it has its own biochemistry with fibrous proteins that allow the cell to contract. Heart cells contract by virtue of the delicate interplay of the ion pumps and channels and the chemical and electrical differences across the membrane.