As the BBC points out, veterinarians and zoologists have noted for almost a century that emotional trauma (usually from being captured by humans or threatened by predators) can cause heart failure in animals as diverse as birds, moose, and otters. But, even though psychiatrists have argued for a while that humans can suffer similar physical pain as a result of emotional trauma, only recently has actual scientific research been able to back this up with hard evidence.
In the last few decades, researchers have come up with a growing amount of data suggesting that acute emotional distress can lead to a heart attack. One study found that January 18, 1991, the beginning of the Persian Gulf War and the date that Iraq pointed its nuclear missiles at Israel, was associated with a higher number of heart attacks in Israel than any other date in the months immediately before or after. Another found a similar spike in cardiac arrests in L.A. directly following a massive earthquake there in 1994.
Most telling, the BBC describes a strange case of a 44-year-old woman in Massachusetts who had all of the symptoms of a heart attack (pain in her left arm and her chest), but tests showed that her arteries were completely clear. The doctors discovered that her son had committed suicide earlier that day, suggesting her emotional trauma had manifested as a very real physical condition.
Even in the wake of considerable evidence, it took the medical community until 2005 to officially recognize the concept of "stress cardiomyopathy" (also known as "broken heart syndrome") — in which emotional stress causes the left ventricle of the heart to swell, resulting in something that looks and acts like a heart attack. However, Johns Hopkins notes that, while broken heart syndrome is a very real and very serious (even potentially fatal) condition, most patients recover quickly and completely under a doctor's care. One thing is clear: An unhappy you, it turns out, translates to an unhappy heart. (BBC)