the.com/echocardiography

means A diagnostic test that uses ultrasound waves to create a moving image of the heart, showing its chambers, valves, and blood flow in action.

from Built from three Greek pieces: 'echo' (sound bouncing back), 'kardia' (heart), and 'graphein' (to write or draw) — so, literally, 'drawing the heart with bounced sound.' The echo part nods to the same principle as sonar: send a pulse, measure what comes back, and turn the delay into a picture. The technique itself is a 20th-century medical development, built on wartime advances in ultrasound and sonar technology that were later turned toward the body instead of submarines.