A heart-monitoring device the size of a 50p piece is being fitted to cardiac patients in Sussex.
The sleuth transmits heartbeat information for clinical analysis
The "sleuth" is implanted under the skin. Every heartbeat is recorded over two years and the results are wirelessly sent to clinicians.
It is being trialled on people who suffer from unexplained fainting in order to see if their condition is linked to any heart problems.
Patients in Eastbourne are said to be Europe's first to have sleuths fitted.
Dr Neil Sulke, from the cardiac unit at the town's hospital, said: "The device allows us to monitor every heartbeat and this is really important in people who faint.
"Many people faint once or twice a year and it's very hard to find out what's going on because they're nowhere near an ECG machine.
"This is their own portable cardiologist that's with them all the time."
The sleuth takes 15 minutes to fit with the patient only needing a local anaesthetic.
They take home a wireless internet transmitter which plugs into their phone line and sends the heartbeat data to a control centre.
Dr Sulke said it was hoped the trial would improve the diagnosis and treatment of unexplained fainting.