Heart rate sensors including high-aspect-ratio photodetector elements (212, 912, 1012, 1112, 1212, 1312, 1312, 1512, 1612, 1712, 1812) are discussed herein. Such high-aspect-ratio photodetector elements may provide improved signal-strength-to-power-consumption performance for heart rate sensors incorporating such photodetector elements as compared with heart rate sensors incorporating, for example, square photodetector elements.