Our aim was to compare the effects of the divalent cations, namely magnesium, zinc, and manganese on the arterial blood pressures and heart rate of guinea pigs. Eighteen guinea pigs weighing 500-700 g were divided into three groups (six in each group), and three divalent cations as sulfate salt (MgSO4, ZnSO4, MnSO4) were administered to all animals after 20-min period of stabilization and at three escalating concentrations (10(-6), 10(-5), 10(-4) mol/kg intravenously, respectively) in 25-min intervals. Each animal received only one kind of cation. Arterial pressures and heart rate were measured and their derivatives were calculated (dp/dt). Our study showed that divalent cations lowered the arterial blood pressures. No significant differences were between groups for systolic, diastolic, and mean pressures, except that 10(-4) mol/kg ZnSO4 was lethal. The heart rates values of ZnSO4 (202 +/- 9) was significantly (P < 0.05) lower after 10(-6) mol/kg than MgSO4 (230 +/- 7). Three divalent cations caused to decrease on arterial pressures. Zn2+ caused cardiac arrest in the highest dose. Intravenous administration of Mn2+ and Mg2+ seems to have similar effects on arterial blood pressures and heart rate. Further work is needed to relate effects on Mn2+ for their possible use in the emergency department.