M-Mode was the earliest form of cardiac ultrasound used clinically. It displays the amplitude signals of various structures along the length of ultrasound beam with distance or depth on vertical axis against the time dimension on the horizontal axis. [Fig. 1.2(a) and (b)]

Main features and advantages are:

1)  High sampling rate allows for accurate evaluation of  rapidly moving valvular structures and endocardium.

2)  High temporal resolution that  allows visualization  of minute changes in wall or valve motion.

3)  Accurate and reproducible measurements of various chamber dimensions and wall thickness.