Hydroxyethyl starch (HES) solutions are commonly used for volume replacement in cardiac surgery patients. The degree of impairment of the haemostatic system depends on the molecular weight and substitution degree of HES solutions. It is claimed that as HES 130/0.4 (Voluven(®)) exhibits a lower in vitro molecular weight and a lower degree of hydroxyethyl substitution than HES 200/0.5 (HAES-steril(®)) therefore it has less impact on haemostasis. A best evidence topic in cardiac surgery was written according to a structured protocol to verify this statement. The question addressed was: in cardiac surgery patients does volume replacement with Voluven(®) impair coagulation less than other colloids? Using the reported search 12 papers, three in vitro and nine clinical studies, were found to represent the best evidence to answer the clinical question. The nine clinical studies were all randomised controlled trials. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The in vitro studies suggest that HES 130/0.4 has no significant effect on platelet variables, shows a faster clot formation process and a better clot retraction as compared with the other HES solutions. On the other hand, current best available evidence (level 1b) from clinical studies, limited by heterogeneity predominantly in terms of dosage of HES 130/0.4 administered and the sample size of individual trials, overwhelmingly suggests that HES 130/0.4 compared with HES 200/0.5 or gelatin-based volume replacement fluid affects coagulation to the same extent resulting in similar degree of blood loss. It can be concluded that contrary to in vitro studies HES 130/0.4 in clinical practice has comparable effects on blood loss after cardiac surgery.