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Introduction Currently, a dose of protamine equal to 1 mg for each 100 units of heparin given is used to reverse the residual heparin activity following off-pump coronary artery bypass. We hypothesized that a 1:1 ratio (ratio of protamine to heparin) could be higher than necessary inducing post-operative disturbance of hemostasis. Methods Between January and March 2014 in 9 patients undergoing off-pump coronary artery bypass, we evaluated the effect of a dose of protamine equal to 1 mg per 100 units of heparin (Total Calculated Dose) on hemostasis as evaluated by means of thromboelastomery. Two data analyses were performed: the first after the administration of 2/3 of the Total Calculated Dose of protamine and the second after the administration of the Total Calculated Dose of protamine. Results We found that the administration of 2/3 of Total Calculated Dose of protamine was always able to reverse the anticoagulant effect of heparin and that a significant clotting time elongation was induced by the infusion of the second part of the Total Calculated Dose of protamine. No modification in clot firmness was observed. Conclusions The present study seems to suggest that the commonly applied ratio equal to 1:1 (ratio of protamine to heparin) could be higher than needed with potential and hazardous impacts on the efficacy of the coagulation system.