Objective To explore the risk factors for ventilator-associated pneumonia (VAP) in the patients over 70 years old after heart surgery and investigate the characteristics of the related etiology so as to guide clinical rational use of antimicrobial agents. Methods Clinical data of 33 elderly patients (over 70 years old) with the duration of mechanical ventilation more than 48h after cardiac surgery in our ICU from January 2013 to June 2014 were collected and retrospectively analyzed. The cohort was assigned into VAP and non-AVP groups, and their clinical data were compared and analyzed to screen the risk factors of postoperative VAP, pathogenic bacteria and their sensitive drugs. Results In the 33 patients, there were 16 patients having VAP. Univariate analysis showed that significant differences were seen in the scores of Acute Physiology and Chronic Health Evaluation Ⅱ (APACHE Ⅱ), aorta blocking time, extracorporeal circulation time, mechanical ventilation time and length of ICU hospitalization between the VAP and non-VAP groups (P＜0.01). Multivariate analysis indicated that aorta blocking time and duration of mechanical ventilation were significantly associated with VAP. Among the 19 isolated strains of pathogenic bacteria, most of them were Gram-negative bacilli (84.2%). Klebsiella pneumoniae and Pseudomonas aeruginosa were the most common ones. The incidences of Gram-positive cocci and fungi were quite low. The antibacterial activity of vancomycin was 100% to Gram-positive cocci. Conclusion A variety of risk factors are related to postoperative VAP in the elderly patients after cardiac surgery. We clinicians should improve surgical skills to shorten the duration of mechanical ventilation and aortic cross-clamping time and use antimicrobial agents rationally so as to improve the prognosis of VAP in the elderly after cardiac surgery.