Back towards the end of the 1800s, the Brown family from Exeter, Rhode Island were experiencing a pattern of deaths due to "consumption," which is an older term for what we now call tuberculosis. Tuberculosis is an infection that generally affects the lungs, and it commonly is the cause of chronic cough with blood, night sweats, fever, and weight loss.
Mary Brown, the mother of the household, was the first to contract consumption and it was the eventual cause of her death. In 1883, her death was followed by the eldest daughter of the family, Mary Olive. And as if that was not enough, just a few years later, in 1891, daughter Mercy Brown and son Edwin Brown both contracted the infection. Things were just not looking up for the poor Brown family from RI.
Tuberculosis was not well understood back in the late 1800s, and there was still much superstition surrounding the disease. It was believed that one of the deceased family members - either Mary, Mary Olive, or Mercy - was a vampire (although the term 'vampire' wasn't used) and that they were causing the illness in the suffering Edwin. The belief back then was that multiple deaths in a family could be linked to the undead, and so the family and friends of the Browns felt the illness affected Edwin because of undead activity from someone else in the family.
After persuading the father of the household - George Brown - to give permission to exhume the bodies, villagers, a doctor, and a newspaper reporter exhumed the bodies on March 17, 1892 to see if they could find signs of any undead activity. The bodies of Mary and Mary Olive both had sure signs of decomposition - consistent with being buried for several years. But when the body of Mercy Brown was exhumed - the most recently deceased of the family, mind you - the team found that her body was relatively unchanged since her death! She even has blood in her heart and her liver - and it was because of this that Mercy was assumed to be a member of the undead, and her reign of terror over her brother Edwin must be put to an end! (The lack of decomposition of her body was attributed to her body being stored in more freezer-like conditions from being stored in an above ground crypt or receiving vault).
So as per the superstition, there was only one thing that could be done to stop Mercy - her heart was removed from her chest, burned to ashes, and then the ashes were mixed with water. You already know where this is going: the mixture was given to the sickly Edwin to drink, and it was believed that the drink would end Mercy's control over Edwin and heal him before he met the same unfortunate fate. The "potion" unfortunately did not work, and Edwin passed away just two months later - another victim of tuberculosis in the Brown family. What was left of Mercy's body was buried at the Chestnut Hill Baptist Church cemetery in Exeter, RI in 1892, where she still remains today.