The heart reacts to any thyroid dysfunction: it will either speed up in case of an overactive thyroid or slow down in the presence of an underactive thyroid. Without treatment thyroid disorders worsen existing heart diseases or cause new ones.
The thyroid produces hormones which are essential for keeping your heart working as it should. The most important thyroid hormones are thyroxine (T4), and triiodothyronine (T3). T3 is the more active thyroid hormone and responsible for growth, development, and virtually all cellular processes. It regulates the heart rate, pulse, blood circulation, heart contractility and oxygen consumption.