AZD8233 is a proprotein convertase subtilisin/kexin type 9 (PCSK9) antisense oligonucleotide under development for treatment of hypercholesterolaemia. A prespecified concentration-QT analysis was performed based on data from a single ascending dose study that was prospectively designed to act as a TQT study substitute. Subcutaneous single doses ranging from 4 to 120 mg were evaluated in 73 adult healthy male subjects. Time-matched 12-lead digital ECG and plasma concentrations (n = 15) were measured at baseline and up to 48 hours after dose in each subject. The analysis was performed using a linear mixed effect model, where change from baseline QTc (ΔQTc) was a dependent variable and time-matched AZD8233 concentration was an independent variable. The high clinical exposure scenario was defined as 1.7-fold the expected Cmax following an assumed therapeutic dose of 60 mg, which corresponds to AZD8233 plasma concentration of 1.39 μg/mL. Estimated placebo-corrected and baseline-adjusted QTcF interval (ΔΔQTcF) at this concentration was -2.2 ms (90% CI: -4.11, -0.28). Furthermore, the upper 90% ΔΔQTcF confidence interval was estimated to be below 10 ms at all observed concentrations. As the effect on ΔΔQTcF is below the threshold for regulatory concern (10 ms), it can be concluded that AZD8233 does not induce QTcF prolongation at the high clinical exposure scenario.