The widespread expression of ion channels and their ability to significantly modulate cell function makes them attractive drug targets. Therapeutic agents which target ion channel proteins comprise the third best selling class of prescription drugs with US sales in 2002 estimated at $12 billion. Somewhat surprisingly the discovery of many marketed ion channel modulators was serendipitous rather than rational and these therapies target relatively few (less than 10) of the 400 ion channel genes contained within the human genome.