Studies show that 48 percent of people can develop depression following a heart attack. But experts say this depression may not be purely psychological. After a cardiac event, the heart may be unable to pump blood as efficiently—causing patients to lose energy.

In addition, chemicals are released in the brain that can work to physiologically cause mood changes. Interestingly, the same study showed that women who suffer heart attacks are 20 percent more likely to develop depression.

The good news: most of these cases can be treated with anti-depressant drugs.