What does cardio mean?
Cardio is an informal English noun for exercise that primarily improves the heart and circulatory system, especially aerobic activity such as running, cycling, swimming, or brisk walking. The term is short for “cardiovascular” and is widely used in gyms, fitness classes, and casual conversation: people say they “do cardio,” while instructors offer cardio workouts or cardio training. It generally refers to sustained activity that raises the heart rate, although the expression is also used more broadly for cardiovascular conditioning. Cardio is usually treated as a mass noun in this sense rather than a countable category, and an individual session is often called a “cardio session” or “workout.” The word’s medical roots are visible in related forms such as cardiac, cardiology, and electrocardiogram. Derived from Greek kardia, meaning “heart,” cardio is useful because it names a familiar fitness concept while retaining a clear connection to medicine and anatomy. In everyday use it is informal but universally understood in English-speaking fitness settings.
nounAn informal shortened form of cardiovascular exercise, especially aerobic activity that raises the heart rate and conditions the heart and circulatory system.
- Exercise that primarily conditions the heart and circulatory system, especially aerobic activity performed to raise the heart rate.
"She did some cardio before work to clear her head."
"We finished the class with twenty minutes of cardio."
"Her doctor recommended regular cardio as part of a healthy lifestyle."
The plural is grammatically possible but uncommon; “cardio sessions” or “cardio workouts” is usually more natural.
"The timetable includes two cardios on Saturdays."
Greek kardia meant “heart”; the modern gym word turned that same root into a shorthand for making your heart work hard.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does cardio come from?
Cardio descends from the English combining form cardio-, which comes from Greek kardia, “heart,” a cognate of Latin cor. The medical combining form underlies related English words such as cardiac and cardiology. The familiar standalone noun is a shortening of cardiovascular, in the sense of cardiovascular exercise, and developed through late-20th-century fitness usage.
Related word forms
How cardio is actually used
Informal in both British and American English and especially common in fitness contexts. It is usually treated as a mass noun when referring to exercise in general, although it can be countable when referring to individual sessions or workouts.
Easily confused with cardio
Cardio usually names exercise or a workout, whereas cardiac means relating to the heart and is common in medical terms.