Echocardiography is a technique using very high frequency sound (called ultrasound) to visualize cardiac anatomy. Sound waves can be transmitted in gas, liquid or solid medium. When it passes a border between two substances of different density, part of the sound will be reflected back.

A probe attached to the echocardiographic machine contains a transducer which emits and records ultrasound. Normally, the transducer placed in various positions over the heart (see figures 32a, 32b, 32c-1) sends ultrasound through the chest wall, heart muscle and blood vessels.
The ultrasound is reflected back to the transducer probe, as it hits various interfaces. The distance between the probe and various interfaces can be calculated by comparing the time it takes the echo to return to the probe against a calibrated time. This information allows a display of the different depths of the various interfaces relative to the probe position (figure32b).

In two dimensional echocardiography the probe emits pulses in various directions. The returning or reflected echos are compiled and graphically displayed as a pie slice, with the apex of the pie closest to the probe, and the remainder of the picture is a composition of depth date from various pie-shaped sections of tissue, analogous to viewing a darkened room by moving a flashlight back and forth in front of you to build a complete picture.

Different two dimensional views of the heart are obtained by moving the probe into various positions such as parasternal (short and longaxis), apical four chamber views, etc (see fig. 32d, 33, 34a, 34b, 35a, 35b, 35c-1).

More detailed views can obtained using high frequency miniature probes inserted into the esophagus to image the heart from inside the body (trans esophageal echocardiography, see figure 145).