右为成年人卵圆孔未闭的探查。 一根金属探针将房间隔掀起以显示未闭开放。正常情况下，左心房压力较高使得卵圆孔闭合。但如果肺动脉高压（如肺栓塞）引起右心房压力上升，卵圆孔就可能开放甚至血栓可以从右心房通过卵圆孔到达左心房。这是一个十分罕见的“反常栓子”（请看本图左边），之所以这样称呼是因为这种在静脉循环中出现的血栓会栓塞于体循环。
At the right is a probe patent foramen ovale in an adult. A metal probe lifts the septum secundum and reveals the opening. Normally, the left atrial pressure keeps the foramen closed, but if right atrial pressures rise with pulmonary hypertension (as with pulmonary embolus), the foramen may open and even allow a thrombus to go from right to left. This is a "paradoxical embolus", rare (seen on the left here), and so called because a thromboembolus arising from the venous circulation can end in the systemic circulation.