van der Vring JA (1999). „Combination of calcium channel blockers and beta blockers for patients with exercise-induced angina pectoris: a double-blind parallel-group comparison of different classes of calcium channel blockers. The Netherlands Working Group on Cardiovascular Research (WCN)”. Angiology. 50 (6): 447—454. PMID10378820. doi:10.1177/000331979905000602.|access-date= захтева |url= (помоћ)
van der Vring JA (1999). „Combination of calcium channel blockers and beta blockers for patients with exercise-induced angina pectoris: a double-blind parallel-group comparison of different classes of calcium channel blockers. The Netherlands Working Group on Cardiovascular Research (WCN)”. Angiology. 50 (6): 447—454. PMID10378820. doi:10.1177/000331979905000602.|access-date= захтева |url= (помоћ)