This prospective study investigated whether pretreatment with intravenously administered calcium would influence the effect of nifedipine on rest hemodynamics and treadmill performance in patients with ischemic heart disease. Seventeen patients were studied after undergoing a qualifying treadmill exercise test that revealed ST segment depression indicative of ischemic heart disease. Study subjects performed three additional treadmill tests as part of the protocol. One treadmill test was obtained from each patient to provide baseline measurements without a preceding intravenous infusion and in the absence of all antianginal drugs including nifedipine; two additional exercise tests were preceded by an infusion and 10 mg of bite-and-swallow nifedipine. The infusions, administered in a randomized, double-blind, crossover fashion, consisted of either 10 ml of 10% calcium chloride (13.6 mEq) in 50 ml of 5% dextrose in water or 5% dextrose in water alone. Rest systolic blood pressure (134 +/- 4.6 mm Hg) was unchanged after placebo infusion (135 +/- 4.6 mm Hg) but decreased to 124 +/- 4.1 mm Hg (p less than 0.01) 25 min after nifedipine administration. Rest systolic blood pressure increased after calcium infusion (from 139 +/- 4.3 to 148 +/- 4.8 mm Hg, p less than 0.01) and then decreased significantly 25 min after nifedipine administration to 135 +/- 4.2 mm Hg (p less than 0.01). Despite a decrease at the time of peak nifedipine effect after either infusion, systolic blood pressure was significantly lower after administration of nifedipine alone than after administration of calcium and nifedipine (124 +/- 4.1 vs. 135 +/- 4.2 mm Hg, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)