Slowed Heart Rate
A slowed heart rate is also one of the most common symptoms of an underactive thyroid gland (hypothyroidism).
If a person has too much or too little thyroid hormone in their body and it’s affecting the metabolism, this will show up as a slowed heart rate. An underactive thyroid gland produces less T3 and T4 than it should, which causes a slowdown in the metabolism and other signs, including fatigue, weight gain, and depression.
On the other hand, if they have an overactive thyroid gland (hyperthyroidism), then there will be excess levels of T3 and T4 circulating through the system. These signals to the hypothalamus that there is enough energy available for activity, which results in an increased heart rate due to increased activity levels.
