The maintenance of angina control was assessed in this multicenter (three sites), randomized, double-blind, parallel-group study. Patients with stable angina pectoris receiving twice-daily sustained-release (SR) diltiazem were switched to equivalent doses of once-daily controlled-delivery (CD) diltiazem or to diltiazem SR. Patients who were switched from diltiazem SR to diltiazem CD (n = 28) experienced a 5% increase in time to termination (p = 0.0004) on the exercise tolerance test (ETT), as well as an 8% improvement in time to onset of angina (p < 0.0001) on the ETT. A similar trend was observed in patients randomized to diltiazem SR (n = 7), which suggested a training effect, and, therefore, equal efficacy between diltiazem SR and diltiazem CD. During exercise testing in the diltiazem SR baseline phase, 77% of the patients did not experience angina, whereas 60% of the patients did not experience ST-segment depression. Following transfer to diltiazem CD, 79 and 61% of patients, respectively, remained angina- and ST-segment depression free. No significant changes in the number of angina attacks, nitroglycerin use, or any hemodynamic-related parameters were observed following transfer to diltiazem CD. Eleven percent of the patients receiving diltiazem CD experienced treatment-related adverse events, which were limited to headache and abdominal pain; these adverse events did not lead to discontinuation of treatment. These findings suggest that patients whose angina is controlled with twice-daily diltiazem SR can be safely and effectively switched to an equivalent daily dose of the once-daily diltiazem CD.