Acidosis has been reported to cause ST-segment elevation. We presented a woman with a history of rectal adenocarcinoma experienced cardiac arrest during the contrast-enhanced computed tomography examination. When spontaneous circulation returned, arterial blood gas revealed she had severe respiratory acidosis, and bedside electrocardiogram showed ST-segment elevation in anterior precordial leads. Emergent coronary angiography was normal. Echocardiography revealed no abnormality of cardiac cavity size, segmental wall motion, or pericardial echo. Carcinoma metastasis in the peritoneal cavity and lungs was detected on the contrast-enhanced computed tomography scan while the heart was not involved. The ST-segment regressed and the respiratory acidosis was corrected after she received mechanical ventilation which strongly suggested the association between acidosis and the electrocardiogram changes.