People who are obese are likely to have fast heart rates. They have high levels of adipokines, cell signaling proteins released by fat cells that can have adverse effects on the cardiovascular system. Fat cells also produce hormones including leptin, which regulates the amount of fat stores in the body and also impacts the cardiovascular system. After weight loss surgery, leptin concentrations drop, and so does a person's heart rate, says Rushikesh Shah, MD, who is completing his training in internal medicine at Upstate. He wrote a paper on this subject for the BMJ Case Report reminding doctors of this "physiological compensatory change" to help avoid unnecessary diagnostic tests and medical interventions.