IPA: /ˈkɑːrdiəˌɡræf/
KK: /ˈkɑrdɪəˌgræf/
A device that records the movements of the heart to help monitor its function.
The doctor used a cardiograph to check the patient's heart activity.
Cardiograph → It is formed from "cardio-" (from Greek "kardia", meaning heart) and "-graph" (from Greek "grapho", meaning to write). The word "cardiograph" refers to a device that writes or records the activity of the heart.
Think of 'heart' ('cardio-') being 'written' or 'recorded' ('-graph') — that's what a cardiograph does.