If you're here with us, you've probably been told by your doctor that you have a hole in your heart. Your first reaction - How am I still alive? Where's the hole exactly? Is this why I was picked last for sports? Okay, let's break it all down. 

If you have a hole in your heart, it's been there your whole life. In fact, when we're first born, we all have a hole in our heart - namely, the foramen ovale. The foramen ovale is a small hole in the septum, creating a channel between the right and left atria (top chambers).
Before we are born, our lungs are out of action (because we're in fluid) - we get all our oxygen via our mother's circulation through the placenta. The foramen ovale acts as a shortcut, allowing the circulation to bypass the lungs whilst continuing to spread blood around our little growing bodies. 

When you take your first breath, the lungs expand open, and the change in pressures swings the foramen ovale shut- this creates a closed right heart circuit and a closed left heart circuit meaning that the blood has to go through the lungs. Pretty neat, huh?

Unfortunately, the foramen ovale's mechanism of closure is pretty shoddy - and 25% of people are left with a small hole between the right and left atria (...it could be you!).
This is called a PFO (Patent Foramen Ovale) and in the vast majority of cases it causes no issue. The left-hand side of the heart is so much stronger than the right, that the high pressure system prevents oxygen-depleted blood from the right side leaking across into the nice, oxygen-rich blood before it shoots around the body. 

However, if the PFO is on the bigger side - or if the pressure of the right-side increases (such as secondary to pulmonary hypertension caused by obstructive sleep apnoea) - a lot of oxygen-depleted blood can leak across and mix with the oxygen-rich blood. This is called a shunt. The blood in the left ventricle is meant to be 100% oxygenated, but with this oxygen-depleted blood in the mix, the percentage decreases and can lead to shortness of breath. 

A PFO can cause another sneaky problem, namely a stroke. Young people who experience a stroke are often in the 25% of those with a PFO. Why you ask? Okay, let's make this simple. 

No PFO: Clot forms in a vein in the calf after a long flight. Clot dislodges and travels back to the right atrium. Clot moves into the right ventricle, and then is pumped into the lung vessels. This is now called a pulmonary embolism (lung clot). If it's small, it'll likely cause minimal symptoms. 

With a PFO: Clot forms in a vein in the calf after a long flight. Clot dislodges and travels back to the right atrium. Clot slips across the PFO and enters the left atrium. Clot moves into the left ventricle, and then is pumped into the brain. Now, we have a stroke. 

A PFO will be found on an echocardiogram with a bubble study. An ultrasound probe is held on the chest, looking at the heart's septum. Meanwhile, bubbly salt water is injected into the vein. A few seconds later, the bubbles appear in the right atrium and we see where they go. Simple. 

If discovered, and causing symptoms, a PFO can be closed surgically. 

Another type of hole in the heart is a VSD (Ventral Septal Defect). A VSD is a common heart malformation, commonly seen in Down's syndrome, amongst other things. A VSD is similar to a PFO but it is a hole between the right and left ventricle. If discovered, it too can be closed surgically.