Your heart has four chambers, co-ordinated together to pump and receive blood from the body and the lungs. Connections between these chambers are colloquially referred to as ‘holes in the heart’ – sometimes normal, and sometimes not.

The four chambers in the heart are separated by thin pieces of tissue. The two atria (top chambers) are separated by a very thin atrial septum, and the two ventricles (bottom chambers) are separated by the thicker ventricular septum. The right ventricle pumps to the lungs via a tube called the pulmonary artery, and the left ventricle pumps toward the body through a tube called the aorta. These two tubes are not normally connected in adults.

Instead of calling them ‘holes’, it’s better to think of them as connections; when these connections are inside the heart they are holes in various walls, whereas if they occur outside the heart they are often in the form of vessels or tubes. You may also hear the word shunt, a word which means to push something away. In this case, blood is pushed from one part of the heart to another through a shunt.

An abnormal connection can occur at each of these levels; between the atria (a patent foramen ovale or an atrial septal defect), between the ventricles (ventricular septal defect), or between the aorta and pulmonary artery (patent ductus arteriosus).

The two sides of your heart

The right side of your heart is the ‘venous’ side – it receives all the blood from the veins of your body, which drain blood away from muscles and organs once they have used the oxygen. It then passes this blood to your lungs.

The left side of your heart is the ‘arterial’ side – it takes the oxygenated blood from your lungs and pushes it to your body.

Connections we are all born with

When we are fetuses, we bypass our lungs and receive oxygenated blood from our mother. There are two ways blood is shunted away from the lungs in utero:

1. Foramen ovale

The foramen ovale is a hole in the atrial septum. Everybody has one as a fetus; when we take a first breath, the change in pressures inside the heart closes this hole. In 20-25% of people, this small hole can remain either completely or partially open (patent foramen ovale, or PFO). This isn’t usually a problem, however in a small percentage of people, things can pass through this hole.

2. Ductus arteriosus

The ductus arteriosus connects the pulmonary artery (the tube coming out of the right ventricle going to the lungs) to the aorta (the tube coming out of the left ventricle going to the body). Although this normally closes over in the majority of people, this can very rarely stay open (ariund 1 in 2000 people), and in that case is called a patent ductus arteriosus, or PDA.

 

Abnormal connections

Congenital defects are abnormal connections that a small percentage of people are born with. It’s easiest to think about these at each level of the heart – between the top chambers (atria), between the bottom chambers (ventricles), and between the outlet tubes (the aorta and pulmonary artery).

Atrial septal defects are abnormal connections between the two atria. They come in a few different forms, based on their location.

Ventricular septal defects occur between the two ventricles. Similarly, they can occur in a two different locations.

 

As mentioned above, the connection between the aorta and pulmonary artery, the ductus arteriosus, can remain open in certain people.

Complications

There are two main problems with a connection between the two sides of the heart:

1. Paradoical emboli

Clots can form in the venous system of the body, often in the legs (called deep vein thrombosis). Clots may go to the lung and cause pulmonary emboli, but if they are small the body can dissolve them. If there is an abnormal connection however, the clot may go to the body (particularly the brain) instead of the lungs, causing a stroke.

2. Shunting

Shunting is where the flow of blood is significantly altered. If the flow is from left to right, then oygenated blood goes back to the lungs, and this extra flow is too much for the fragiel blood vessels in the lungs. Eventually, they can become severely damaged. If the flow is from right to left, then de-oygenated blood that was supposed to go to the lungs goes to the body, and the organs and muslces do not receive enough oxygen.

The size and severity of these shunts can be measured with echocardiography (usually transoesophageal echocardiography) and right heart catheterisation.