Off-pump coronary artery bypass grafting (OPCABG) was introduced many years ago aiming to reduce the known complications of conventional on-pump coronary surgeries. Heparin is required during the procedures, but the available protocols have diverse dosage regimens. The primary objective of this systematic review is to examine the effect of different heparin doses on the outcomes of OPCABG.

MEDLINE and EMBASE were searched. Four reviewers identified eligible clinical trials. Two reviewers extracted data and independently assessed the risk of bias using Cochrane tool. The primary outcome was the activated clotting time (ACT) at three minutes. The secondary outcomes were proportion of patients requiring blood products and the length of hospital stay. An aggregate data approach was used.

Three single-center randomized studies recruiting 256 patients were included. The studies compared low-dose (1.5–2 mg/kg) and high-dose (3 mg/kg) heparin boluses. The overall mean difference for ACT after three minutes between low- and high-dose heparin is – 126.16 (95% CI: – 142.19, – 110.14). The proportion of patients requiring blood products after surgery [odd ratio 1.27 (95% CI: 0.69, 2.32)] or the overall length of stay [mean difference −0.15 (95% CI: −0.84, 0.53)] did not differ between the heparin doses.

In OPCABG, high-dose compared with low-dose heparin did not affect the utilization of more blood products or increased the overall length of stay. Unsurprisingly, ACT values were higher in the high-dose heparin group. Larger and adequately powered randomized clinical trials are indicated to resolve the uncertainty.