The prefix "cardi-" refers to the heart. There are several synonyms for this prefix, such as "cardio-," "cardiac-," and "cardiovascular-." "Cardio-" is often used to refer to physical exercise that is good for the heart, such as cardio workouts. "Cardiac-" is a medical term used to describe the heart, such as cardiac arrest or cardiac surgery. "Cardiovascular-" refers to the heart and the blood vessels that transport blood throughout the body, such as cardiovascular disease or cardiovascular health. Overall, the use of these synonyms helps to better understand the different aspects and functions of the heart.