A 56-year-old man was brought to our tertiary medical center unconscious after collapse at home from out-of-hospital cardiac arrest and successful resuscitation. Return of spontaneous circulation was achieved after the delivery of 2 shocks with an automated external defibrillator. On arrival at the emergency department, the patient was in deep coma with Glasgow Coma Scale score of 3. An electrocardiogram revealed ST-segment elevation in lead augmented vector right, depression in leads V3-V6, and hypokinesis of the anterior cardiac wall. An acute myocardial infraction was suspected. Prompt treatment was essential, otherwise it would be fatal. The patient was intubated and immediately scheduled for a coronary arteriography (CAG) and revascularization, which involve certain amount of radiation exposure. The patient presented with his 14-year-old daughter and 11-year-old twin sons and without any adult relatives or legally authorized representatives. His wife had died from gastric cancer 3 years earlier. The patient had undergone a left lobe thyroidectomy for a pT1N0M0 papillary thyroid carcinoma 8 years prior. Quite unexpectedly, when providing collateral history, his daughter revealed that she and the patient held sincere beliefs against any radiation exposure. She refused to approve with any medical procedures requiring radiation exposure for her father. Her testimony was deemed credible because she stated that he and his family evacuated far from his hometown following the Fukushima nuclear disaster. This was despite his residential area being publicly declared scientifically safe and not warranting evacuation. She further mentioned that he had previously refused any procedures involving radiation. The daughter also reported that, as far as she knew, the patient did not have a formal document to expressing this belief. We were faced with an apparent conflict between the daughter’s testimony regarding the patient’s strong opposition to radiation exposure and the principle of beneficence: respecting a patient’s potential opposition to radiation exposure or proceeding with the best medical care including emergency CAG. While expressing empathy for the 14-year-old’s concerns, an attending physician patiently and clearly explained the circumstances. The attending physician discussed with the daughter that her father’s condition was life-threatening and that the radiological examination and intervention were crucial to save her father’s life. This resonated with the daughter. She eventually agreed to permit definitive treatment to her father for the suspected acute myocardial infarction, keeping radiation doses “as low as possible”. We attempted to contact the patient’s older sister repeatedly, but she did not answer the calls. Collectively, the care team reached a consensus that we should proceed with our planned treatment as we considered this the best possible medical care. Emergency CAG showed subtotal occlusion of left main coronary artery. The patient was diagnosed with acute myocardial infarction and percutaneous coronary intervention for the left main coronary artery disease was performed. Standard protocols, designed to minimize radiation exposure as a matter of routine, were followed. Target temperature management was applied in the intensive care unit (ICU) for 24 h. Three days after admission, the patient was able to follow commands and was successfully extubated. Screening tests revealed that neurocognitive impairment was minimal. The day after ICU admission, the medical team was finally able to reach the patient’s sister and explained the overall situation. She described what he had been like in detail; he has always been extremely particular about foods; he has avoided foods that are potentially radiation-contaminated as much as possible since a young age. She did not have a belief against radiation exposure, and completely agreed with all the actions we had taken. Because the patient was comatose and no other legally authorized representatives were available besides her, we acknowledged that she was a surrogate. Although she did not actively participate in decision-making, she would have been an appropriate and legally designated surrogate if we had been able to reach her earlier. We still felt comfortable with her agreeing with our decisions. Once the patient regained consciousness, he accepted and appreciated the treatment he had received to save his life. He disclosed that he had previously declined screening procedures requiring radiation and declined further procedures requiring radiation exposure. Our ethics committee reviewed the case and determined that the team’s decision and decision-make process were reasonable. The patient was discharged from the ICU after 10 days and returned home 4 days later without any complications. A telephone interview was conducted with the patient 2 months after the event. He was still grateful for the actions we had taken. He mentioned that his belief against radiation exposure was not derived from a religious belief but was still a fervent and profound belief. The patient stated that he would permit the best possible medical care with a “minimum” radiation exposure level if a similar situation were to arise in the future.