Heart rate in humans during underwater swimming with and without breath-hold

Heart rate was monitored, by way of radiotelemetry, from 6 male subjects of mean age (±SE) 24 ± 1 years and of mean mass 73.5 ± 2.5 kg. Measurements were made in a 25 m pool at a water temperature of 28°C. Resting heart rate was 67 ± 3.7 beats · min−1 and when the subjects submerged themselves completely in the pool, but remained inactive, there was a prompt, gradual reduction in heart rate which reached 48 ± 2.6 beats · min−1 within 30 sec and...