Objective: To compare the effect of a calcium antagonist and a beta-blocker on left-ventricular diastolic function in patients with ischemic heart disease. Methods: 138 patients with chronic stable angina pectoris were randomized in a multicenter, double-blind trial to treatment with either mibefradil or atenolol for 6 weeks (50 mg once daily for 2 weeks followed by 100 mg once daily for 4 weeks). The ratio between early (E) and late (A) diastolic mitral flow velocities (E/A), the E wave deceleration time (DT) and the left ventricular isovolumetric relaxation time (IRT) were measured by Doppler echocardiography as parameters of left-ventricular diastolic function initially, after 4 and after 6 weeks of treatment. Results: Mibefradil did not change the E/A ratio significantly (+4%, NS), while atenolol treatment resulted in a significant increase in the E/A ratio (+20%, p < 0.001). Mibefradil treatment, on the other hand, resulted in a significant decrease (–8%, p < 0.001) in IRT, while atenolol treatment did not change IRT. Neither mibefradil nor atenolol treatment changed DT significantly. Conclusions: Both mibefradil and atenolol treatment significantly improves echocardiographic indices of left-ventricular diastolic function in patients with chronic stable angina. However, they affect different parameters and thus apparently act through different mechanisms.