OBJECTIVE To evaluate national practice for antibiotic prophylaxis in cardiac surgery with respect to the use of protocols, agent selection and duration of administration. METHODS Two point-prevalence surveys of intensive care units in 24 public and 27 private hospitals performing cardiac surgery in Australia, conducted in 2004 and 2008, using a structured telephone questionnaire of the attending senior intensive care clinician in each unit. METHODS Existence of a protocol in the unit for antibiotic prophylaxis, specific antibiotic agents used and their duration of administration. RESULTS Between 2004 and 2008, reported protocol use increased from 58% to 80% (P = 0.02), while concordance with version 13 of the Australian Therapeutic guidelines: antibiotic for both choice of agent and timing (duration of administration) remained around 10%. Use of multiple agents was common, as was continued antibiotic administration after completion of surgery. Over 4 years, the proportion of cardiac surgical units reporting vancomycin administration for routine valve surgery prophylaxis doubled to 62% (P < 0.001). CONCLUSIONS Despite an increase in reported protocol use for antibiotic prophylaxis in cardiac surgery, concordance with national antibiotic guidelines remained low, with duration of antibiotic administration deviating most from recommendations. Prophylactic vancomycin use appears to have increased substantially in recent years. Clinical implementation of recommended perioperative cardiac surgical antibiotic prophylaxis may not occur until supported by evidence from either a large prospective randomised study or standardised national surveillance of cardiac surgical site infection rates.