MR thermometry can be used for MRI-guided cardiac ablations, but ECG-triggering is not always effective. We propose to use the Active Tracking (AT) functionality included in the catheter to prospectively trigger the thermometry measurements. Modules measuring the position of the AT microcoil were interleaved with a thermometry sequence, which were repeated until a trigger condition is detected. Experiments showed successful triggering in a beating heart phantom, with a temperature stability of 1.12±0.36°C. For in-vivo interventional application, respiratory motion will need to be taken into account.