cardi(o)-

The heart.

Greek kardia, heart.

The medical study of the heart is cardiology, practised by a cardiologist; an electrocardiogram (Greek graphein, write), or ECG, is a record or display of a person's heartbeat, created by an electrocardiograph. Several adjectives relate to the heart as part of the wider body system; these include cardiovascular (Latin vasculum, a little vessel) for the heart and its blood vessels, cardiopulmonary (Latin pulmo, pulmon‑, lung) for the heart and lungs, and cardiothoracic (Greek thōrax, chest) for the heart and chest. Outside medicine the most common compound is cardioid for a heart-shaped curve in mathematics.