A Doppler ultrasound is a test that uses high-frequency sound waves to measure the amount of blood flow through your arteries and veins, usually those that supply blood to your arms and legs. And it is a risk-free and pain-free procedure that requires little preparation. A regular ultrasound uses sound waves to produce images, but it can’t show the blood flow. A Doppler ultrasound may help diagnose many conditions including blood clots, heart valve defects and congenital heart diseases, a blocked artery (arterial occlusion), decreased blood circulation into your legs (peripheral artery disease), poorly functioning valves in your leg veins, which can cause blood or other fluids to pool in your legs (venous insufficiency), bulging arteries (aneurysms) and narrowing of an artery, such as in your neck (carotid artery stenosis).