Modified Look-Locker inversion recovery (MOLLI) as a commonly used myocardial T1 mapping approach shows high precision and reproducibility. Its limited capability in multi-slice acquisition per breathhold prolongs examination time in cases of desired full left ventricular coverage. The previously proposed fast single-breathhold 2D multi-slice myocardial T1 mapping (FAST1) technique can achieve time-efficient full left ventricular coverage at 1.5T. In this work, this capability of FAST1 at 3T is optimized and characterized. Compared to MOLLI, FAST1 can yield 4-fold increase of spatial coverage, limited penalty of T1 spatial variability, no significant difference of T1 repeatability and linearly correlated T1 values.