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Figure 3 Ammonium chloride (NH₄Cl) during demand ischemia. Ischemia (decreasing coronary perfusion pressure [CPP] to 20 mm Hg) reduced left ventricular systolic pressure (LVSP) to 60 mm Hg and left ventricular end-diastolic pressure (LVEDP) to 18 mm Hg. Tachycardia increased LVEDP to 25 mm Hg, indicating increased diastolic chamber stiffness. 50 mmol/L ammonium chloride (50 mM NH₄Cl) imposed after tachycardia during sustained ischemic diastolic dysfunction initially increased LVSP from 63 to 80 mm Hg, then reduced it to 56 mm Hg, indicating a positive, followed by a negative, inotropic effect, consistent with its known effects on intracellular pH and, hence, myofilament calcium-sensitivity. Elevated LVEDP, however, remained unchanged, implying that it was not increased by a calcium-activated mechanism.