the.com/electrocardiogram

means A recording of the heart's electrical activity, traced as a line of peaks and dips that shows how steadily and strongly the heart is beating.

from Built from Greek parts: 'elektro-' (electricity, itself from 'elektron,' amber, which sparked when rubbed), 'kardia' (heart), and 'gramma' (something written or recorded). The device that produces it, the electrocardiograph, was developed in the late 1800s and early 1900s, notably refined by the Dutch physiologist Willem Einthoven, who built the string galvanometer sensitive enough to catch the heart's faint electrical whispers and turn them into a readable line.