A heart rate monitoring apparatus and related method for detecting the successive beats of a heart and providing a reliable estimate of heartbeat rate. The apparatus measures the time intervals between the successive beats and averages a prescribed number of the most recently occurring measurements. The particular measurement that differs most from the computed average is adjusted to be equal to that average, and the adjusted set of measurements is then averaged. These latter steps of adjusting and averaging are repeated a prescribed number of times, and the last-computed average is displayed as an estimate of heartbeat rate. The entire procedure is repeated upon the occurrence of each successive heartbeat.