A heart rate monitor implements power saving algorithms while monitoring a subject's heart rate. The monitor continuously monitors a subject during an initial period to determine an initial heart rate. After the initial heart rate is acquired, power may not be provided for portions of the monitor until a heart beat is expected to occur. At some point before the expected heart beat occurs, power is returned to the components which have not received power. The expected heart beat is then detected, and power to selected portions of the monitor is terminated again until another expected heart beat approaches in time. By providing power to monitor components just before an expected heart beat, the monitor may still detect the heart beat and determine the corresponding heart rate of the user. The period of time during which power is terminated for some components may be determined from the detected heart rate. The number of heart beats during which power is terminated for selected monitor components may vary.