Extreme bradycardia and tachycardia in the world's largest animal

We present a major advancement in our ability to bring the physiological laboratory to the open ocean through the noninvasive use of a suction cup-attached tag equipped with surface electrodes. Our study provides heart rate data of a large, free-diving whale (blue whale) without prior capture or restraint. We recorded a wide range of heart rates from the tag, reaching only several beats per minute during deep foraging dives (bradycardia) and nearly 40 beats per minute at the sea surface (tachycardia) as the whale recovered from its oxygen debt. The latter likely represents maximal heart rate given the measured duration of the heart beat itself, thereby demonstrating the greatest dynamic range in cardiac activity at this scale.