Acute chest pain and troponin changes in middle-aged individuals can pose a diagnostic challenge, as age-related vascular changes may complicate common inflammatory and infectious conditions, affecting outcomes. Nevertheless, research on vaccine-related myocardial injury and systemic inflammation causing acute coronary syndrome (ACS) remains limited when compared to the extensive literature and advances in ACS. A 52-year-old man presented to A&E with a 2-3-day history of right-sided chest pain after receiving a flu vaccination. The pain radiated to his right shoulder and eventually to his central chest. He developed a fever after the vaccination and managed it with hydration and rest. He had a history of hypertension, dyslipidaemia, and ischaemic heart disease diagnosed by coronary angiogram in 2019. His electrocardiogram showed atrial fibrillation with a fast ventricular response, which was successfully chemically cardioverted. An angiogram revealed acute total thrombotic occlusion of the intermediate coronary artery branch. He underwent cardiac magnetic resonance imaging, improved, and was discharged with dual antiplatelet therapy and outpatient follow-up. This case underscores the need to consider ACS in patients with high pretest probability of coronary heart disease, even with a strong suspicion of myocarditis. A thorough history, ECG, high-sensitivity troponin, echocardiography, and coronary angiography are key in assessing high-risk chest pain. Inflammatory heart conditions may independently increase the risk of acute plaque disruption and thrombotic occlusion leading to myocardial infarction.