You might feel your heart rate increase as you crank out dozens of push-ups, but they don't really count as cardio training. Cardio exercise, as per the American College of Sports Medicine, must meet three parameters: It must use your major, large muscle groups, such as your legs, hips and back; be rhythmic in nature; and be maintained continuously.
While push-ups do use large muscles and can be rhythmic, you really can't maintain them continuously. For cardio to be truly beneficial, you need to do at least 10 minutes consecutively. This contributes to the minimum 150 minutes per week considered to be essential for good health.
Push-Ups as Strength Training
Most people can only pump out a dozen or so push-ups before their muscles fatigue. Even extremely fit people who perform multiple sets and reps of the move are exhibiting muscular strength -- the ability for their muscles to work against resistance -- and muscular endurance, which is the ability to sustain work against resistance for a long period of time.
During a push-up, you build strength and endurance primarily in the muscles of the chest, shoulders and triceps. Your core also gets a good workout as it stabilizes your trunk during the push-up.
Typical exercises considered to be cardiovascular training are jogging, pedaling an elliptical trainer, cycling, swimming and walking. However, you can break out of these classic examples and include ballroom dancing, water aerobics, cross country skiing, playing tennis and gardening.
You just can't keep push-ups going for long enough to maintain an elevated heart rate for 10 minutes or longer. Even 100 consecutive push-ups takes just two to three minutes to complete by the most fit of folks; if it takes you 10 minutes to complete these, then you're most likely not maintaining a substantially elevated heart rate to count as cardio.
Include Push-Ups in a Cardio Workout
While push-ups alone don't qualify as cardio, they can be part of a calisthenics circuit that keeps your heart rate elevated for a sustained period of time. For example, do each of the following exercises for 60 seconds each to create a 10-minute cardio circuit:
Before starting these exercises, warm up with three to five minutes of marching in place. Alternatively, do a set of 10 to 20 push-ups, then a minute of a high-intensity cardiovascular exercise, such as the high knees, for 10 minutes to create a simpler cardio circuit that is more push-up centered.