Lithium is frequently used in the treatment of bipolar disorders and is known to induce ECG alterations. This case study describes various patterns of lithium-induced ECG modifications in a patient with acute-on-chronic lithium intoxication. Clinicians should be familiar with this problem as it can have life-threatening consequences and lead to important changes in patient's management. Our patient was admitted for acute delirium with an ECG showing atrial fibrillation with wide QRS and ST-segment elevation. These modifications were first mistaken for an acute myocardial infarction and a diagnosis of Brugada syndrome was finally reached. Treatment after the acute phase implied changes in the therapeutic modality and required frequent monitoring.