Under the normal stress response, the body releases myriad hormones. But if someone is under extreme stress, and these hormones are released in very significant amounts, it can cause damage to the heart muscle, eliciting acute heart failure, causing the heart to distend and pump inefficiently. In rare cases, this can lead to cardiovascular collapse and even death.
This is called broken heart syndrome because in most cases it's precipitated by a period of extreme stress, such as during a divorce, after the death of a loved one, during pregnancy, or concurrently with some other emotional stressor.
The syndrome also has an obvious gender inequality to it, with the overwhelming majority of victims being relatively healthy adult women with no other cardiovascular problems.
Most patients head to the emergency room because they're worried about a heart attack, experiencing the same symptoms, such as chest pain, irregular heart rate, and dizziness. They're treated accordingly (such as with oxygen, blood thinners, and medications), but further investigation discovers no other cardiovascular issues, such as blood vessel disease. With other causes of heart failure ruled out, the patient is diagnosed with broken heart syndrome.
Thankfully, if managed and treated appropriately, the syndrome typically resolves in days or weeks, and most make a full recovery. But without treatment, abnormal heart rhythms, stroke and, in rare cases, even death can result. For example, when I was in training as a cardiovascular surgery fellow, we implanted a temporary support “mechanical heart” in a woman that suffered from this syndrome due to severe problems during her delivery. She recovered about a week later allowing us to remove the devices, and thankfully did well, but she did require major invasive surgery to sustain life. And in a poorly equipped center she may not have been so lucky.