A best evidence topic was written according to a structured protocol. The question addressed was whether incidentally found patent foramen ovale (PFO) during isolated coronary surgery should be closed. A total of 573 papers were found using the reported searches of which six represented the best evidence to answer the clinical question. The authors, date, journal, study type, population, main outcome measures and results are tabulated. There is currently no evidence to suggest that incidental PFO in patients undergoing cardiac surgery is linked with increased morbidity, mortality or decreased long-term survival. The most significant study identified examined the outcomes of 2277 patients with incidentally found PFO during cardiac surgery of whom 639 underwent closure. After propensity matched analysis, the authors found closure was associated with a significantly higher risk of postoperative stroke with no advantage in terms of long-term survival. A recent survey of 438 cardiac surgeons from the USA showed no consensus on decision-making behind closure, but that factors taken in to account include PFO size, right atrial pressure and a history of paradoxical embolism. This is not surprising given that morphological research has confirmed that larger PFO size is indeed associated with cryptogenic stroke.