Quantitative myocardial perfusion MRI is potentially powerful for diagnosing coronary artery disease. However, It is challenging to accurately measure dynamic contrast enhancement throughout the whole moving heart. Most perfusion methods employ some combination of ECG-triggering, breath-holds, dual-bolus acquisition, and multislice 2D acquisition, leading to difficult workflows and limited spatial coverage. Here we describe a non-ECG, free-breathing, single-bolus, 3D alternative which employs the MR Multitasking framework to perform low-rank tensor imaging. We add 3D respiratory motion compensation to this framework to eliminate the need for breath-holds. This new method is demonstrated and evaluated in healthy volunteers.