In the article, "Compartmentalization of Cardiac Beta-Adrenergic Inotropy Modulation by Phosphodiesterase Type 5" by Takimoto et al (Circulation. 2007;115:2159-2167), 4 errors appeared. (1) In Table 1, line 4, "dPdtmax, mHg/s" should have read "dP/dtmax, mm Hg/s." (2) In Table 1, line 6, "CO, μl/min" should have read "CO, mL/min." (3) In Table 2, line 5, "dPdtmax, mHg/s" should have read "dP/dtmax, mm Hg/s." The authors regret these errors. (4) In Table 2, line 2, "dPdtmax, IP/s" should have read "dP/dtmax/IP, s^-1. The publisher regrets this error. This correction has been made to the current online version of the article. A formal correction will appear in a future issue of the journal.