Potassium ions (K+) play a critical role in cardiac electrophysiology; changes in their concentration might reflect ongoing pathophysiological processes related to cardiovascular diseases. In vivo potassium (39K) MRI, due to its extremely low sensitivity remains a major challenge. Here we investigated, for the first time, the feasibility of in vivo 39K MRI of human heart in a healthy subject. To achieve this goal, we developed a custom-built 39K/1H RF coil, which is tailored for 39K MRI of human heart at 7.0 Tesla. This approach facilitated 39K MRI of human heart with an isotropic spatial resolution of 14.5 mm3 within a total scan time of 30 minutes.