A child presented with headache, dizziness, intermittent claudication with occasional dyspnoea.The most probable diagnosis in –
Clinical manifestations of COA 

Symptoms of coarctation of aorta occurs due to decrease in blood supply distal to aortic obstruction.
If obstruction is distal to left subclavian artery, manifestations are due to arterial insufficiency to lower limbs.
Intermittent claudication
Pain
Weakness of Leg
Dysnea on running
Weak pulses and lower BP in the lower extremities --> Delayed or weak impalpable femorals compared to strong brachial arteries.
Collateral circulation develops between precoarctation arterial branches and the post coarctation arteries through enlarged intercostal and internal mammaty arteries.
This produces radiologically visible erosions (notching) of undersurface (inferior) of ribs.
Hypertension --> Headache, dizziness.
If the obstruction is proximal to left subclavian artery ---> Blood supply to left arm (supplied by left subclavian) is interrupted whereas blood supply to right arm is normal -* Pressure difference in two arms.

Murmur in coarctation of aorta 

The blood passing through the narrowed aorta —> Midsystolic murmur in anterior part of chest, back and spinous process.
When lumen becomes severly narrowed the blood flow through it, turns into a high velocity jet -p Continous murmur.
COA is associated with bicuspid aortic valve in 50-80% of patients. The bicuspid valve produce aortic regurgitation Diastolic murmur.
ASD
PDA
TOF
Coarctation of aorta