In medical matters of the heart, your mind can be either your best friend or your worst enemy. What you think and feel — and how well you deal with those feelings — can affect your physical health in myriad ways.

If you have trouble working off the tension of life’s daily crises and frustrations, you may be putting your heart at risk with lower-level but constant stress

The National Institute of Mental Health estimates that between 40 and 65 percent of patients who’ve had a heart attack have some form of depression.

Your anger can be killing you, say researchers who have studied the relation between cardiac risk and feelings of hostility. A study by Swedish scientists, for instance, found that both social isolation and suppressed anger impair the heart’s ability to vary its rate in response to daily stress. And those who nurture feelings of distrust and resentment toward others are also probably contributing to the isolation that makes their recovery difficult.