A method and apparatus for monitoring a patient's heart rate sense first cardiac events in a heart chamber using a first cardiac electrode pair and sense second cardiac events in the heart chamber using a second cardiac electrode pair. The method includes estimating a first heart rate using the first cardiac events, comparing the first heart rate to a heart rate threshold and estimating a second heart rate using the second cardiac events in response to the first heart rate exceeding the heart rate threshold, determining whether the second cardiac events are unreliable, and setting the second heart rate equal to the first heart rate in response to the second cardiac events being unreliable.
