The Short Version
This claim is a widely circulated myth. Major medical authorities — including the Mayo Clinic, Cleveland Clinic, Northwestern Medicine, and the American Academy of Sleep Medicine — explicitly state that waking a sleepwalker does not cause heart attacks, brain damage, or other serious medical harm. The only documented risk is temporary confusion or disorientation, which in rare cases may lead to minor accidental injury. The heart attack component is categorically unsupported by clinical evidence.