Name: Cardio Drift
Rating: 3.8 (8 reviews)
Author: momoTM

This data field app calculates cardiovascular drift as percentage change between pace and heart rate ratio (PaHR-%) in the first and second half of the workout at the current time. Data field value is updated once a minute and calculations are done only when the timer is on. So this is an almost real time PaHR calculator of your cardiovascular fitness and dehydration level. Aerobic cardio workout target value is said to be 5% or below but can vary greatly due to various environmental and individual factors. Just google with words "cardiac drift", "aerobic decoupling" and "cardiovascular drift" to find out more.
Cardio Drift data field app data draws a nice graph for those every one minute data values on Garmin Connect web site so that you can see the history of those values and how they have changed during your workout. Every value is calculated for the first and second half of the duration time of the workout. In the beginning of the workout like warming up you normally see great variation of the values as a normal sign of physiological cardiovascular response but after that over time you begin to see some upward drift of the values especially with constant pace. You may see negative values as a sign of negative drift, too. Negative values may be shown in a smaller font as they are not as important as positive drift values to observe but this depends on device.
You may install this data field as any other data field app. Using it is easy. Just press Start button to start your workout and you will see 60 s countdown. After that this data field is updated once a minute and saved in your workout data file.
If you are interested in PwHR (power/heart rate ratio) version of this app check out my Cardio PwHR Drift app.
Enjoy!