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• cardio
  cardio

  noun

  aerobic exercise that stimulates and strengthens the heart and lungs.
• cardio-
  cardio-

  a combining form meaning “heart,” used in the formation of compound words.

cardio

¹ American  

[kahr-dee-oh] / ˈkɑr di oʊ /

noun

Informal.

1. aerobic exercise that stimulates and strengthens the heart and lungs.

   I mostly use weights, but I always add a little cardio into my routine.

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adjective

Informal.

1. of or relating to aerobic exercise.

   The class begins with a slow and steady warmup, and then it switches to a cardio workout.

2. of or relating to the heart; cardiovascular.

   He's a hugely successful cardio surgeon.

cardio- ² American  

1. a combining form meaning “heart,” used in the formation of compound words.

   cardiogram.

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cardio- British  

combining form

1. heart

   cardiogram

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Usage

What does cardio- mean? Cardio- is a combining form used like a prefix meaning “heart.” It is used in many medical and scientific terms. Cardio- comes from the Greek kardía, meaning “heart.” In fact, the English word heart and the Greek kardía are related. Learn more at our entry for heart. What are variants of cardio-?When combined with words or word elements that begin with a vowel, cardio- becomes cardi-, as in cardiectomy.

Etymology

Origin of cardio¹

First recorded in 1960–65

Origin of cardio-²

< Greek kardio-, combining form of kardía

Example Sentences

Cardio activities such as running, swimming, and dancing appear to be especially effective at easing symptoms of depression and anxiety.

From Science Daily • Feb. 16, 2026

Cardio is not just good for my heart, but is a great emotional release and gets my endorphins going.

From The Wall Street Journal • Jan. 5, 2026

Cardio is important—but resistance training is where it’s at.

From Slate • Jan. 1, 2025

Cardio and weightlifting have become a part of my routine once the writers’ strike began.

From Los Angeles Times • Oct. 29, 2023

Cardio and abdominal exercises are his favorite, but sessions could include anything to improve his strength and mobility.

From Seattle Times • Nov. 5, 2021