The antianginal efficacy of molsidomine (single oral dose of 2 mg), a new antianginal drug, was evaluated in 12 patients with coronary artery disease in a double-blind randomized placebo-controlled study by bicycle ergometry. Besides the standard ergometric parameters, the myocardial efficiency index (MEI) was determined from the ratio of the maximum workload (kgm/min) to double product (mm Hg·min)· 10-<sup>2</sup>, normalized for body surface area. Compared to placebo, molsidomine decreased positive exercise tests by 50%, pain response by 66%, and the magnitude of ST depression by 43%. Furthermore, the onset of ergometric positive response was delayed, with an increase in maximum workload achieved (+21 %), total work performed (+43%), and duration of exercise (+28%). MEI also increased from 0.98 ± 0.43 to 1.18 ± 0.44 (p < 0.005), due to a significant increase in maximal workload without a parallel increase in double product. These findings suggest that molsidomine is an effective antianginal drug and improves myocardial efficiency in patients with angina due to coronary artery disease.