Complete Heart Block and Massive Pericardial Effusion as the Presenting Manifestations of Metastatic Colorectal Adenocarcinoma.

backgroundColorectal cancer is the most prevalent gastrointestinal cancer in Asia. Cardiac metastasis is exceedingly rare, and clinical detection during life is low as most cases remain clinically silent. CASE SUMMARY: A 41-year-old woman with a history of locally advanced rectal adenocarcinoma, who previously underwent upfront surgery and adjuvant chemotherapy, presented with progressive dyspnea and recurrent syncope. Evaluation revealed complete heart block and a large pericardial effusion. Pericardial fluid drainage was immediately performed, and a permanent pacemaker was subsequently implanted, resulting in clinical improvement. DISCUSSION: This case highlights extensive cardiac infiltration manifesting 2 life-threatening cardiac manifestations in a recurrent rectal adenocarcinoma, underscoring the importance of immediate interventions. TAKE-HOME MESSAGES: In retrospect, the absence of total neoadjuvant therapy in the initial management may have contributed to early recurrence of rectal cancer. Prompt and coordinated multidisciplinary interventions are crucial in a critical cardiac metastatic disease to improve survival and quality of life.