In medical terminology, what does the root word "cardio" refer to?

The root word "cardio" comes from the Greek word "kardia," which specifically means "heart." In medical terminology, prefixes and suffixes are combined with root words to denote specific aspects of health and anatomy. For instance, terms like "cardiology," the study of heart diseases, or "cardiovascular," which pertains to the heart and the system of blood vessels, illustrate how "cardio" is utilized to refer to the heart. This understanding is fundamental in the medical field, as it aids in deciphering and comprehending various medical terms related to cardiovascular health and diseases. The other options refer to different components of the circulatory system and muscular anatomy, each with their specific root terms.