What causes bradycardia and then tachycardia?

Bradycardia, characterized by a slower than normal heart rate, can be caused by factors such as increased vagal tone, certain medications, or underlying health conditions like hypothyroidism or heart block. It can lead to a compensatory response where the heart may subsequently experience tachycardia, or a faster than normal heart rate, as the body attempts to maintain adequate blood flow and oxygen delivery. This shift can also occur due to stress, anxiety, fever, or other physiological demands. Essentially, the body’s mechanisms to regulate heart rate can switch from slowing down to speeding up in response to various stimuli or conditions.