Which of the following statements about coronary heart disease (CHD) is true?

A) Attempts to reduce depression in CHD patients through the use of antidepressants have been highly successful.
B) Heart rate variability is not a risk factor for CHD.
C) Exercise is effective in reducing both CHD and depression.
D) Increased heart rate variability is an indication of poorer functioning of the autonomic nervous system.

Exercise has been shown to be effective in reducing both CHD and depression. Option A is false as studies have shown mixed results regarding the efficacy of antidepressants in reducing depression in CHD patients. Option B is false as reduced heart rate variability has been identified as a risk factor for CHD. Option D is false as increased heart rate variability is actually considered a sign of better functioning of the autonomic nervous system.