Myocardial T1 mapping provides quantitative tissue characterization for the assessment of various cardiomyopathies. However, currently available myocardial T1 mapping techniques still have several limitations such as insufficient coverage, low spatial resolution, and the need of acquiring the data under multiple breath-holds. To overcome these problems, here we propose a free-running (free-breathing, no ECG gating) 3D whole heart T1 mapping technique with high isotropic spatial resolution. This approach allows for myocardial T1 mapping at arbitrary cardiac phases, enabling high-resolution dynamic T1 maps. The feasibility of the proposed sequence was validated against conventional methods in phantom and five healthy subjects.