Narwhal hearts beat slowly in panic, and that's probably not a good thing

Narwhals are easily recognized by their long tusk,
but this isolated species of toothed whale has been hard to research.
We know a little about them, but their physiology and metabolism
are still a puzzle to marine biologists
Using a specially engineered device that resembles an undersea “fitness tracker,”
researchers received some seemingly paradoxical data
in wild narwhal vital signs.
In most mammals, the flight response they undergo in reaction to danger
causes the heartrate to increase,
in order to help blood flow to the muscles,
and supply the oxygen needed during a speedy retreat.
For land mammals, oxygen is plentiful in the environment,
But because aquatic mammals can’t breathe water, they have to hold their breath.
To help conserve this stored oxygen, they also lower their heart rate.
This decrease when diving is not unusual.
Narwhals usually bottom out around 10 beats per minute,
but the researchers saw that as they swam away,
their heart rate went much lower,
to under 4 beats per minute.
The problem is that in these flight situations, narwhals get the conflicting signal
to both dive quickly and beat their hearts slowly,
As a result, their oxygen supply gets used up very fast,
sharply decreasing the amount of time they can dive.
In lab animals subjected to this same paradoxical physiology, sudden death can occur.
Researchers aren’t sure how these extended periods of hypoxia affect the narwhals health,
and with the increased incursion into their environment by humans,
these periods may become more frequent.
For now, biologists will have to figure out
how narwhal bodies deal with this type of stress,
and if anything can be done to prevent more of it.
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Narwhal hearts beat slowly in panic, and that's probably not a good thing

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