The <em>Polar</em> <em>F4</em> <em>heart</em> <em>rate</em> <em>monitor</em> helps keep fitness enthusiasts in the correct zone for optimized training benefit. Visually follow the time in your target <em>heart</em> <em>rate</em> zone via the fitness bullets displayed. Set your <em>heart</em> <em>rate</em> limits and stay informed