Morgan analyzed the heartbeats of soldiers and sailors before they experienced major stress. Sure enough, the ones with metronomic heartbeats performed the best in survival school and underwater navigation testing. They also did the best in what's called close-quarters combat training. Morgan analyzed their heart rates right before they went into mock battle. They were all suited up in combat gear, waiting for a buzzer to ring that would send them running into a building to "kill" the enemy and rescue hostages. (They use "simunitions," simulated ammunition that hurts but doesn't cause real harm.) The ones with metronomic heartbeats, Morgan says, shoot more bad guys and kill fewer hostages. Unfortunately, this metronomic effect is usually associated with early heart disease and even sudden death. Morgan wonders whether the same thing that makes you really good at surviving under high stress may not translate into excellent heart health when you're 50.
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