Abstract

The foramen ovale is a natural interatrial channel, which normally closes soon after birth when pressure in the left atrium comes to exceed that in the right atrium. However, in about 30% of the population, the foramen stays patent throughout life, providing a potential channel through which blood may shunt from the right to the left atrium (Hagen et al. 1984). Over the past 15 years, several studies have shown that a patent foramen ovale (PFO) is detected more frequently in patients with an otherwise unexplained ischaemic stroke than in control subjects, or in patients with an identifiable cause of stroke (Lechat et al. 1988; Webster et al. 1988; Overell et al. 2000). However, the nature of the link between this common cardiac abnormality and stroke is unclear (Mas 1996). The difficulty in proving a causal relationship between PFO and stroke in the individual patient, and the lack of randomized