The most common cause of vascular obstruction is a blood clot, also known as a DVT. This type of vascular problem usually occurs in one leg (not both), and leads to swelling of the soft tissues throughout the foot and ankle. The swelling can also extend further up the leg.
The hypothalamus is a part of your brain that controls body temperature. When you exercise, your body temperature increases, causing the hypothalamus to signal the brainstem to further increase your heart rate.
A fever can increase the body's heart rate, especially if the fever is high. Fevers can also cause sweating, shivering or chills, which can make the body feel too cold, causing the heart beat faster as it tries warm up the body.