The response to verapamil alone and combined with isosorbide dinitrate in a group of 12 patients with severe ischemic heart disease and stable effort angina was assessed by means of serial treadmill testing. The study was randomized, of a square latin design and double-blind. The tested drugs and dosages were 120 mg of verapamil, 120 mg of verapamil plus 20 mg of isosorbide dinitrate and placebo. Patients were serially tested (Bruce protocol) over three consecutive days at 8-9-12 and 16 hours. A significative improvement was observed in several ischemic parameters both with verapamil alone and combined with isosorbide dinitrate, but this improvement was remarkably enhanced with the combination of drugs. The mean exercise time to produce angina improved from 268 +/- 18 sec (basal) to 379 +/- 19 sec (verapamil plus isosorbide dinitrate) and the time for 1 mm ST segment depression from 163 +/- 22 sec (basal) to 257 +/- 19 sec (verapamil plus isosorbide dinitrate) when measured at the last daily test (8 hours after drug administration). It is concluded that both verapamil alone and combined with isosorbide dinitrate at the chosen doses are clinically efficient, significantly improving the ischemic parameters. The combination of verapamil and isosorbide dinitrate resulted in a remarkably better improvement in this group of patients with stable effort angina.