A fiber optic plethysmograph (FOP) has been redesigned and used to monitor cardiac activity in real time during apnoea. The device was tested using four healthy subjects aged between 23 and 31, and it is concluded that the device performs reliably. Advanced algorithms have been developed and implemented to perform the cardiac signal extraction. A strong correlation is noted between the signals derived using the FOP and the respiratory inductive plethysmograph (RIP) when the latter has also been applied to monitor cardiac activity. The approach developed for interpreting thoracocardiograms (TCGs) and abdominocardiograms (ACGs) derived from the RIP is therefore directly applicable to the interpretation of the corresponding FOP signals. The prospect of using the FOP system for real-time gating in a magnetic resonance (MR) scanner environment is discussed.