In 1877, Cohnheim first indicated a causal relation between patent foramen ovale (PFO) and relevant sickness when analysing the case of a young woman with a stroke.¹ Since then, PFO has been recognised as a potential conduit for paradoxical embolism of thrombus, fat, air, or “things” as harmless as desaturated blood leading to various ailments, such as cerebral ischaemia,² transient global amnesia, decompression illness in divers,³ refractory hypoxemia in the presence of right ventricular infarction or severe pulmonary disease, and the rare platypnoea–orthodeoxia syndrome. PFO has even been recently linked to the prevalent disorder of migraine with aura,^4,5 and now many experts no longer regard it as a harmless pimple but as a peril to health and even longevity. Thus, the drastic statement can be envisaged that any hole, maybe except for valvar gaps and ventricular or coronary lumens, should be closed as soon as it is detected. Aside from debating the latter mentioned visions, the main goal of this article is to provide a practical overview of how a PFO can be identified best.

RELEVANCE AND PREVALENCE

In contrast to the notion of an abridged life after birth due to an open foramen ovale, the negative effect of a closed foramen ovale before birth is not speculative. The function of the foramen ovale before birth is that well oxygenated blood from the inferior vena cava bypasses the not yet operational pulmonary circulation. In this context, the Eustachian valve causes the blood to stream towards the foramen ovale and directly into the left atrium. During and …