Background <p>Although rare, cardiac metastases are increasingly reported in oncology. Surgery may be an option for selected patients, but is often not feasible due to high postoperative morbidity. Radiotherapy therefore emerges as a non-invasive local treatment, either as a primary or adjuvant approach, similar to its use in other palliative settings.</p> Case presentation <p>We report the case of a patient with a cardiac metastasis from metastatic renal cell carcinoma, initially revealed by a life-threatening arrhythmic storm resulting in cardiac arrest. Given the arrhythmia’s resistance to conventional therapies—including antiarrhythmic drugs and radiofrequency ablation—stereotactic body radiotherapy (SBRT) was administered, targeting the cardiac lesion. This is only the second reported case of SBRT for a cardiac metastasis responsible for severe rhythm disturbances and there has never been a case report of SBRT delivered at such a high dose to a cardiac metastasis of this size. The procedure was well tolerated without immediate complications and showed initial therapeutic efficacy. However, the patient later experienced a recurrence of arrhythmia, which ultimately led to the patient’s death.</p> Conclusion <p>This case highlights the potential role of SBRT as a salvage therapy for cardiac metastases, which remain a challenging and often fatal condition.</p>