What does cardio mean?
Cardio is an informal noun referring to cardiovascular exercise — any sustained physical activity that raises the heart rate and strengthens the heart and lungs. Common forms include running, cycling, swimming, brisk walking, and rowing. The word originated as a casual shortening of 'cardiovascular' and has become the standard everyday term in gyms, fitness apps, and health advice, especially in American English though it is now widely understood across the English-speaking world. It functions as an uncountable mass noun, so speakers say 'do some cardio' or 'a cardio session' rather than counting individual 'cardios.' Because it carries associations of health, energy, and self-care, it tends to have positive connotations, appearing in phrases like 'cardio day' or 'get your cardio in.' While perfectly acceptable in casual speech and journalism, more formal medical writing typically prefers the full terms 'aerobic exercise' or 'cardiovascular exercise.'
nounInformal term for cardiovascular exercise — physical activity that raises the heart rate and strengthens the heart and lungs, such as running, cycling, or swimming.
- Physical exercise that elevates the heart rate and improves cardiovascular fitness, such as running, cycling, or swimming.
"She does thirty minutes of cardio every morning before work."
"He swapped weightlifting for cardio to improve his stamina."
"The doctor recommended regular cardio to help lower her blood pressure."
Cardio is normally used as an uncountable mass noun; a plural form is not standard in careful usage.
"She gets her cardio done early, before the gym fills up."
Short for 'cardiovascular,' this gym-floor favourite traces straight back to the Greek word for the heart — kardia.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cardio
Cardio arose in the twentieth century as a colloquial clipping of 'cardiovascular,' an adjective built on the Greek root kardia, meaning 'heart.' That same Greek root underlies a whole family of English words, including cardiac, cardiology, cardiogram, and myocardium, all of which entered English through scientific Latin formations. The clipped form gained currency in fitness culture, where brevity and informality were valued, and it is now firmly established in everyday English.
How cardio is actually used
Cardio is an informal, chiefly spoken register word, ubiquitous in fitness contexts and everyday conversation but generally avoided in formal medical writing, where 'cardiovascular exercise' or 'aerobic exercise' is preferred. It is used as an uncountable mass noun ('some cardio'), not with an article in most cases.
Easily confused with cardio
Cardiac is a formal adjective relating to the heart itself (e.g. cardiac arrest), while cardio is an informal noun meaning heart-rate-raising exercise.