Last updated: 4 October 2026
Reviewed by Jordan Morley, FA Level 2 Football Coach
Cardiovascular (cardiac) drift is the gradual upward creep in heart rate during prolonged steady-state exercise, even when pace and effort remain constant. It's caused primarily by progressive dehydration reducing plasma volume, and rising core body temperature increasing the cardiovascular demand of cooling. Cardiac drift means heart rate becomes a less reliable pacing guide late in long sessions — a runner holding the same pace may see heart rate rise 10-20 bpm over a couple of hours. Good hydration and heat management reduce drift, and it diminishes with improved aerobic fitness.
- Heart rate rises despite constant pace
- Caused by dehydration and rising core temp
- Makes HR less reliable late in long sessions
- Reduced by hydration and aerobic fitness
In practice
Cardiac drift is why your heart rate can creep up 10-15 beats per minute over a long steady run even though your pace hasn't changed — it's a sign you need more fluids or that the heat is adding real physiological strain, not necessarily that you're overexerting on purpose.
FAQ
Is cardiac drift a bad sign?
Not inherently — some drift is normal on long runs, especially in heat; it becomes a concern mainly when it's extreme or paired with other signs of dehydration or heat stress.
How can I reduce cardiac drift on long runs?
Staying well-hydrated, replacing electrolytes, and training in similar heat conditions to your event (heat acclimatisation) all help reduce the magnitude of cardiac drift.