In a Japanese study, 54 healthy volunteers were divided into two groups, one eating enough tuna and swordfish for 14 weeks to reach the highest level of methylmercury exposure deemed safe by the Japanese government. The methylmercury accumulation was tested from hair samples, and the amount rose steadily over the 14 weeks. The end result for the group that ate the fish is that they had subtle changes to their heart rhythm, although the damage corrected itself as the fish was no longer being eaten. The resting heart rate is regulated by the autonomic nervous system, and methylmercury is a powerful neurotoxicant.
http://www.environmentalhealthnews.org/ehs/newscience/safe-mercury-levels-from-fish-pose-risk-to-heart/
