Some sobering news to take to heart: Cardiovascular disease and stroke are the number one and two killers worldwide, according to the American Heart Association’s 2016 Heart Disease and Stroke Statistics Update. In fact, in the U.S., one in three deaths is from heart disease, stroke, and other cardiovascular diseases. With numbers like that, chances are you know someone whose life was cut short by a heart-related illness. Maybe that’s even one of the reasons why you bought a Fitbit tracker. But did you know there’s another way you can use your device to help gain insights into your cardiorespiratory fitness besides tracking your food, weight, and activity?

If you own a Fitbit Alta HR, Fitbit Charge 2, Fitbit Blaze, or Fitbit Ionic you have access to your Cardio Fitness Score, a unique Fitbit feature that estimates your VO2 max—a measure of how well your body uses oxygen during strenuous exercise.

VO2 max is becoming increasingly important in the heart-health world. In a peer-reviewed Scientific Statement published late last year, researchers writing on behalf of the American Heart Association (AHA) argue that doctors should assess cardiorespiratory fitness (i.e. your VO2 max) as a vital sign in the same way they would metrics like blood pressure and cholesterol. That’s because people with low cardiorespiratory fitness have a 56 percent higher risk of death from heart disease than those who are the most fit, according to a meta-analysis of 33 studies.

In one 2014 study, when researchers took cardiorespiratory fitness into consideration along with traditional risk factors—such as age, BMI, total cholesterol, and smoking—they were better able to predict which men and women had the highest long-term risk of dying from heart disease. Cardiorespiratory fitness, the American Heart Association researchers conclude, may actually be a more powerful predictor of early death than the traditional risk factors mentioned above.

That’s a pretty strong endorsement. And it makes sense. Your aerobic fitness reflects the ability of your body to transport blood from your heart to your muscles, and the ability of your muscles to receive and use that oxygen-rich blood, according to the AHA. Cardiorespiratory fitness involves numerous body systems and so is a good indicator of total-body health.

The first step in taking control of your cardiorespiratory fitness score is to find out what yours is. The best and most accurate way to do this is with a cardiopulmonary stress test at your doctor’s office. However, if this test is too costly or your doctor doesn’t think it’s necessary, the AHA researchers found that estimated cardiorespiratory fitness scores, similar to the one Fitbit provides, are reliable and valid.

Fitbit can calculate your Cardio Fitness Score in two ways. The default method is based on your resting heart rate, age, gender, weight, and other personal information and will show your Cardio Fitness Score as being within a range, like 42-46 in the example below. (For the best results, make sure your Fitbit profile is up to date and your wear your tracker while you sleep, which improves the accuracy of your resting heart rate score.)

To get a more precise cardio fitness estimate, use multisport mode to track a 10-minute (or longer) run on a flat course with GPS. (For instructions on using multisport mode with GPS, see How do I use multisport or exercise mode on my tracker?)

Once Fitbit has determined your Cardio Fitness Score, it will calculate your Cardio Fitness Level, which places your score into one of five ranges—Poor, Fair, Average, Good, Very Good, or Excellent—to demonstrate how your aerobic fitness compares to other people of the same age range and gender.

To find this information, tap the heart-rate tile on your Fitbit app dashboard, then swipe left on the top graph. You’ll see your Cardio Fitness Score here. Click the double arrow in the top right for a more in depth look at your score, including how much improvement you can expect with weight loss and adequate exercise.

If your Cardio Fitness Score is low—like really low—don’t despair. AHA researchers found that exceptionally high cardiorespiratory scores aren’t necessary to experience significant health benefits. In fact, the biggest heart-health gains occur when you graduate from the least fit group to the next least fit group. In other words, modest activity levels can have a big affect on lowering your risk of dying from heart disease.

AHA researchers identified 49 studies that examined how to improve your cardiorespiratory score. Here’s what they found works best for each fitness level:

If you have low cardiorespiratory fitness…do at least 30 minutes of brisk walking three to four times a week. Your heart rate should be in your fat burn target heart rate zone during the session.

If you have intermediate cardiorespiratory fitness…do 30 to 60 minutes of moderate-intensity exercise—such as brisk walking on a flat surface, hiking in hilly terrain, or jogging slowly—five days a week. Your heart rate should be in your fat burn or low cardio heart rate zone.

If you have a high cardiorespiratory fitness…do 20 to 60 minutes of vigorous-intensity exercise (cardio or peak target heart rate zone) three days per week.

In general, intensity matters more than workout duration and frequency when trying to improve your score. According to the AHA study: “The higher the baseline cardiorespiratory fitness, the more vigorous the intensity needed to produce a clinically significant increase.”

For more information on appropriate exercise for your Cardio Fitness Level, check out 5 Simple Ways to Boost Your Cardio Fitness. And remember, you don’t have to be an uber-active athlete to have a healthy heart. Small gains pay big dividends in the cardio-fitness world.