Protamine remains the anticoagulant of choice for cardiopulmonary bypass (CPB). The process of protamine neutralization of heparin came with the side effects sometimes; it can be life threatening or fetal reaction. The adverse cardiopulmonary response of protamine has been observed during entire history of clinical cardiac surgery. The true mechanism reaction is difficult to defined and the complexity of the clinical situation The classification of protamine reaction has been divided in to main 3 types (transient systemic hypotension secondary to rapid administration, anaphylactic and anaphylactoid reaction and catastrophic pulmonary vasoconstriction.

The reaction from pharmacologic histamine release is the most common type of reaction. Protamine was believed to induce hypotension by this mechanism, and it was demonstrated to release histamine by degranulation of isolated mast cells From the hypothesis that the systemic hypotension cause by the released of histamine. The investigators will measure the serum tryptase which is the enzyme that released from degranulation of human mast cell. Comparing the serum tryptase level of the patient at baseline, 30 min and 60 min after protamine was given.

There for the hypothesis of this study is administrating of H1 and H2 blocker helps attenuate the drop in MAP after protamine is given.

Inclusion Criteria:

• ASA physical status 1-3
• Schedule for open heart surgery

Exclusion Criteria:

• History of allergy to the study drugs or protamine
• History of previous cardiac surgery or received protamine
• History of diabetes with insulin therapy

normal saline will be used as placebo in control group