Krum H, Hill J, Fruhwald F, Sharpe C, Abraham G, Zhu JR, Poy C, Kragten JA. Tolerability of beta-blockers in elderly patients with chronic heart failure: the COLA II study. Eur J Heart Fail. 2006 May;8(3):302–7. doi: 10.1016/j.ejheart.2005.08.002. PMID: 16198627.