This is an extension of Echocardiography. Based on complicated physics, this test indicates the direction of the blood flow in a particular area. It is called ‘colour’ Doppler because the three colours red, blue and yellow represent the direction of the blood flow on the echo monitor.
Doppler comes in very useful in detecting and assessing valve leaks, too tight valves, holes in heart walls, etc. Doppler also shows irregular flow of blood across the chamber walls. If blood is passing through the walls of the heart chambers, (through a birth defect, for example) it may be detected by colour Doppler.
Also, in case of birth defects the direction of blood flow may be reversed. Doppler detects this best to give information about the type of the birth defect.