Background <p>Kounis syndrome refers to acute coronary syndrome precipitated by an allergic or anaphylactic reaction that has a slight predominance in male patients. The most frequently reported symptom is chest pain. Kounis syndrome is a rare and frequently underdiagnosed condition that demands a high degree of clinical suspicion. To the best of our knowledge, this is the first reported case of type I Kounis syndrome after the Nuss procedure with clinically obscured chest pain.</p> Case presentation <p>A 32-year-old Taiwanese woman underwent the Nuss procedure and received intravenous Clindamycin and Ketorolac postoperatively. Generalized wheals, pruritus, and shock developed, and she was treated in accordance with the diagnosis of anaphylaxis. Postoperative pain from the Nuss procedure and the use of analgesics masked ischemic chest pain, delaying prompt clinical evaluation. Electrocardiographic findings demonstrated elevation of the ST-segment in the precordial leads V4, V5, and V6 and an elevated high-sensitivity troponin I level. Echocardiography revealed no left ventricular wall motion abnormalities or pericardial effusion. Coronary angiography was omitted because imaging artifacts from the surgical bars introduced during the Nuss procedure limited visual field, compromising its diagnostic value. The high-sensitivity troponin I level improved progressively with conservative treatment. The subsequent hospital course was uneventful, with the patient remaining stable. A diagnosis of Kounis syndrome was established, and the patient was discharged.</p> Conclusions <p>Kounis syndrome is an underdiagnosed disease with newly proposed etiologies but no treatment guidelines. Clinical awareness is essential when treating anaphylaxis given the possibility of concurrent acute coronary syndrome, especially in patients undergoing the Nuss procedure, as chest pain may be masked. Kounis syndrome should be considered alongside other differential diagnoses.</p>