In thyrotoxicosis, the heart rate typically does what?

In thyrotoxicosis, the heart rate typically increases due to the elevated levels of thyroid hormones in the body, primarily thyroxine (T4) and triiodothyronine (T3). These hormones enhance metabolic activity and increase the body's overall energy expenditure, leading to an increased heart rate. This condition stimulates the heart and the cardiovascular system, resulting in tachycardia, which is commonly observed as a clinical manifestation of thyrotoxicosis.

In contrast, a decrease in heart rate would be more characteristic of conditions such as hypothyroidism, where thyroid hormone levels are low and the body's metabolic processes slow down. Similarly, if the heart rate were to stay the same, it would not reflect the typical physiological response to excessive thyroid hormones. Variability in heart rate could occur but is not a standard response in thyrotoxicosis and would rather suggest other underlying issues. Thus, the increase in heart rate is a definitive sign of thyrotoxicosis and reflects the hyperdynamic state induced by the overproduction of thyroid hormones.