Fetal cardiac cine MRI requires an MRI-based cardiac gating signal since recording a fetal ECG is fraught with significant challenges. Existing approaches usually extract the signal from real-time image series and mandate semi-manual user interaction. However, these give often inconsistent results or suffer from reduced spatio-temporal resolution. We propose a novel algorithm which automatically localizes the fetal heart on real-time low-resolution images, and provides a precise frequency estimate of the cardiac motion signal that can be used for gating. We show that this automated method leads to images with equal or better quality than those obtained with the manual approach.