The new device has another advantage, says Grace: it provides a much better view of what's going on inside the heart. Electrical noise inside the heart can confuse ICDs with embedded leads. Currently, Smith says, one in three ICD patients suffers unnecessary shocks because the ICD misinterprets the state of the heart. That should be much less of a problem with the new device, he says.

Cameron's plan is to implant the device in another 55 patients before the end of the year. These will be monitored for a year, and data from the trial will be submitted to the FDA and European authorities.

Cameron believes that despite the additional demand for power, it can get a battery life of about five years out of its device, which is similar to that for existing ICDs. But this will vary on a case-by-case basis, depending on how often a patient has to be shocked, says Smith.

According to figures from Morgan Stanley, more than 200,000 new ICDs are expected to be put in people in 2008, nearly half of those in the United States. According to Grace, Cameron's S-ICDs are likely to have a huge impact on this market by giving patients and physicians more confidence. "I think they will redefine thresholds for implantation, bringing in far more patients," Grace says. "Physicians have rather been put off referring in view of the problems they have seen."