In a 2-year-old boy with untreated cystic fibrosis, an acute deterioration of his chronic respiratory insufficiency developed due to bilateral pneumonia. This condition caused acute right-sided heart failure and nontransmural myocardial infarction of the inferior wall. In concordance with this diagnosis, a marked increase of CPK-MB levels combined with transient severe ischemia on the ECG and the absence of myocardial injury at echocardiography was seen. At 3 years follow-up, he was in good clinical condition.