BACKGROUND: Depression increases mortality of coronary patients, and autonomic dysfunction has been proposed as an explanation for this association. METHODS: In a sample of 38 adults > or = 60 years with myocardial infarction or unstable angina, we studied depression (presence of a major depressive episode and 21-item Hamilton depression score) and heart rate variability (HRV) of 550 normal beats shortly after admission to the coronary care unit (CCU). Thirty patients were alive at 6 months and were studied at that time as well. Spectral HRV measurements included power in the high-frequency range (HF, 0.15-0.55 Hz, a measure of parasympathetic activity) and low-frequency range (LF, 0.03-0.15 Hz). Nonspectral HRV measurements included standard deviation of normal beats (SDNN) and two measures of vagal activity: percentage of adjacent cycles differing by >50 ms (pNN50) and the root-mean-square of differences in successive beats (rMSNN). RESULTS: Patients who died within 6 months (n=8) had a higher Hamilton-D score than survivors (13.9+/-6.5 vs. 18.4+/-5.6, P=0.039) and were more likely to have an episode of major depression upon admission to the CCU (71 vs. 27%, P=0.027). An increase in Hamilton-D score at 6 months correlated with a decrease in total (r=-0.48, P=0.014), high-frequency (r=-0.49, P=0.007), and low-frequency HRV (r=-0.46, P=0.014). LIMITATIONS: Patients belonged to a single institution and there was a small proportion of men. CONCLUSIONS: Progression of mood symptoms 6 months after an acute coronary event is associated with an impairment of autonomic control of the heart in elderly individuals.