Some people with no history of depression seem to become depressed after a heart attack. On the flip side, some people with depression but no heart disease, seem to develop heart disease at a higher rate than others as pointed out by John Hopkins Medicine.

So what’s the link between depression and heart disease?

Studies show depression may be destructive when it comes to blood clotting, blood pressure, heart rhythm and stress hormone levels. This destruction may be why depressed patients with stable cardiovascular disease “are at a two to three times higher risk of dying than similar patients without depression,” wrote The New York Times.

When our hearts are healthy, they contract and expand like a rubber band while pumping blood. However, unhealthy hearts may have tissue that hardens. This is called fibrosis.

The University of Maryland School of Medicine followed 880 people and found that those with depression are more likely to suffer from fibrosis.

Inflammation, which increases heart disease risk and death, may be another link.

Dr. Lauren M. Osborne, assistant professor of psychiatry, Johns Hopkins University, told The New York Times that after giving patients certain medications, doctors had noticed an increase in the level of inflammatory molecules in the blood often coincided with a greater tendency to depression.

An elevated C-reactive protein (CRP) level, has been linked to inflammation of the heart and blood vessels. Inflammation increases collagen production. Collagen’s job is to connect our skin, bones, tendons and muscles. The problem: too much collagen and it stiffens the heart.

The University of Maryland study also showed that depressed people have higher CRP levels than those who do not suffer from depression.

Some experts believe that there is yet another link. Depression can even out the normal ups and downs in heart rate. That’s not a good sign. It means the heart is weaker and less flexible.

Furthermore, mental distress seems to encourage platelets to bunch together.