Echocardiography

Echocardiography is a tool for diagnosing certain types of heart problems. Echocardiography uses ultrasonic sound waves to generate pictures of the heart. Because it uses only sound waves and doesn't involve injecting anything inside the body, echocardiography is a pain-free, risk-free means of looking at the heart.

How it's done

In echocardiography, a "transducer" (a microphone-like object which both transmits and receives the ultrasonic waves) is held against the chest of the patient. The transducer transmits a fan-shaped wave of sound. When the sound reaches the heart, it is reflected back, first by one exterior wall, then by internal structures, and finally by the opposite exterior wall. The "bounce back" signals received by the transducer create a cross-sectional picture of the heart. 

You can find further information here: The American Heart Association Website