Coarctation of the aorta (CoA) is a congenital condition whereby the aorta is narrow, usually in the area where the ductus arteriosus (ligamentum arteriosum after regression) inserts. The word coarctation means "pressing or drawing together; narrowing". Coarctations are most common in the aortic arch. The arch may be small in babies with coarctations. Other heart defects may also occur when coarctation is present, typically occurring on the left side of the heart. When a patient has a coarctation, the left ventricle has to work harder. Since the aorta is narrowed, the left ventricle must generate a much higher pressure than normal in order to force enough blood through the aorta to deliver blood to the lower part of the body. If the narrowing is severe enough, the left ventricle may not be strong enough to push blood through the coarctation, thus resulting in a lack of blood to the lower half of the body. Physiologically its complete form is manifested as interrupted aortic arch.^{[citation needed]}

There are three types of aortic coarctations:

Aortic coarctation and aortic stenosis are both forms of aortic narrowing. In terms of word root meanings, the names are not different, but a conventional distinction in their usage allows differentiation of clinical aspects. This spectrum is dichotomized by the idea that aortic coarctation occurs in the aortic arch, at or near the ductus arteriosus, whereas aortic stenosis occurs in the aortic root, at or near the aortic valve. This naturally could present the question of the dividing line between a post valvular stenosis and a preductal coarctation; nonetheless, the dichotomy has a practical use, as most defects are either one or the other.^{[citation needed]}

In mild cases, children may show no signs or symptoms at first and their condition may not be diagnosed until later in life. Some children born with coarctation of the aorta have additional heart defects, such as aortic stenosis, ventricular septal defect, patent ductus arteriosus or mitral valve abnormalities.^{[citation needed]}

Coarctation is about twice as common in boys as it is in girls. It is frequently found in girls who have Turner syndrome.

Symptoms may be absent with mild narrowings (coarctation). When present, they include breathing difficulties, poor appetite or trouble feeding, and failure to thrive. Later on, children may develop symptoms related to problems with blood flow and an enlarged heart. They may experience dizziness or shortness of breath, fainting or near-fainting episodes, chest pain, abnormal tiredness or fatigue, headaches, or nosebleeds. They have cold legs and feet or have pain in their legs with exercise (intermittent claudication).

In cases of more severe coarctations, babies may develop serious problems soon after birth because not enough blood can get through the aorta to the rest of their body. Arterial hypertension in the arms with low blood pressure in the lower extremities is classic. In the lower extremities, weak pulses in the femoral arteries and arteries of the feet are found.

The coarctation typically occurs after the left subclavian artery. However, if situated before it, blood flow to the left arm is compromised and asynchronous or radial pulses of different "strength" may be detected (normal on the right arm, weak or delayed on the left), termed radio-radial delay. In these cases, a difference between the normal radial pulse in the right arm and the delayed femoral pulse in the legs (either side) may be apparent, whilst no such delay would be appreciated with palpation of both delayed left arm and either femoral pulses. On the other hand, a coarctation occurring after the left subclavian artery will produce synchronous radial pulses, but radio-femoral delay will be present under palpation in either arm (both arm pulses are normal compared to the delayed leg pulses).^{[citation needed]}