Every year, sudden death kills over 100,000 Britons. In the US, that figure is a quarter of a million. Many of the victims have some history of coronary heart disease, but it's not the classic heart attack that kills but a rapid onset of fatal electrical activity in the heart. Horizon follows a bizarre trail to pick up clues to the nature of sudden death.

Transcript: send a cheque for £2.00, payable to BSS, to [address removed]. Health: page 14
Picture Story: page 69
(Ceefax subtitles)