Cardiac T1ρ mapping has shown promising results for detecting ischemic cardiomyopathy without the need of exogenous contrast agents. Current 2D myocardial T1ρ mapping requires multiple breath-holds and provides limited coverage of the heart. In this study, we proposed a free-breathing 3D T1ρ mapping technique featuring whole heart coverage, near-isotropic spatial resolution (1.7×1.7×2mm3) and 100% respiratory acquisition efficiency. With the proposed technique, five T1ρ weightings were acquired in a clinically feasible scan time (~6 min), based on which 3D T1ρ maps were estimated. The accuracy and feasibility of the 3D technique was investigated in phantoms, healthy subjects and patient.