Is a high heart rate problem in altitude mountain climbing?

At high altitudes, the body produces more red blood cells to carry oxygen. This can lead to an increase in the resting heart rate, as the heart has to work harder to pump the oxygen-rich blood throughout the body. The normal heart rate at rest is between 60 and 100 beats per minute, but at altitudes above 8,000 feet, the heart rate can increase up to 120 beats per minute or more. This increase in heart rate is usually harmless and temporary, and will return to normal once the climber descends to a lower altitude.