Background. Deep-sternal infection is a devastating complication after open-heart surgery. However, the association between infection control practices and deep-sternal infection rates is unclear. Methods. To identify contributors to increased deep-sternal infection rates in our institution, consecutive open-heart surgery patients were prospectively studied during two periods (75 and 40 days), including 66 and 40 patients, respectively. Active monitoring including 149 infection control practices was performed in the operating room and intensive care unit. End-points were sternal infection rates and their relation to infection deep-control practices. Results. Mean age was 62 ± 11 years and 68% were males. Coronary bypass was performed in 82%. Clinical and surgical features were comparable, except that patients in period 2 were more likely to have heart failure (15% vs 1.5%, p = 0.01) and had a longer mean duration of surgery (277 vs 217 minutes, p < 0.005). Only 57 practices (38%) were adequately performed. The main categories showing inadequate practices were disinfection, traffic, hand-washing, and surgical attire of non-scrubbed personnel, anesthesiologists, and pump technicians. Many categories showed a statistically significant, improvement between periods. Deep-sternal infection rates in prestudy and poststudy periods were 10% and 2.8%, respectively (p = 0.007). Conclusions. Active monitoring among personnel involved in open-heart surgery resulted in a significant and sustained decrease in deep-sternal infection rates, through modification of human behavior and improvement of performance standards, probably mediated by the Hawthorne effect. Periodic active monitoring may be a valuable tool to achieve and even sustain such a decrease with tremendous implications on morbidity, costs, and quality of care.