Generally patients with hyperthyroidism have an increased heart rate, often greater than 100 beats per minute. If you have hyperthyroidism and bradycardia at the same time, it is important to look for the cause of this condition, for example, if a patient with hyperthyroidism also has sick sinus syndrome, which can cause a fast or slow heart rate. It is also important to be aware of the effects of medications, such as beta-blockers, which can cause bradycardia. There are other conditions, such as problems with the heart muscle itself and problems with heart conduction, which can cause bradycardia.