PFO — Patent Foramen Ovale

A PFO is a small opening between the upper chambers of your heart. This hole is present from birth in about 25% of the population. While many people live without issues, it can allow blood to bypass the lungs.

This bypass means nitrogen bubbles might enter your arterial system directly. Such bubbles can cause decompression sickness (DCS) even if you follow dive tables perfectly. I saw a diver in Koh Tao in 2018 get hit by DCS after a shallow profile because of this condition.

Do not ignore your symptoms. If you have a history of unexplained DCS, ask a doctor for an echocardiogram. A formal medical diagnosis is the only way to know your specific risk level.