Trimethidinium is a bisquaternary amine ganglion blocking agent with antihypertensive actions. Administration of the drug results in a decrease in blood pressure in the systemic and pulmonary arteries and the right atrium. Associated with these decreased pressures, the stroke volume decreased, but there was sufficient increase in cardiac rate so that cardiac output did not change significantly. Both right and left ventricular work decreased significantly while left ventricular myocardial oxygen consumption was unchanged and calculated cardiac efficiency decreased. Associated side effects on the gastrointestinal tract are reported to be mild and easily controlled when compared with those of pentapyrrolidinium and mecamylamine.