Background: Congenital left ventricular aneurysm (LVA) and diverticulum (LVD) are rare cardiac anomalies frequently associated with electrocardiogram (ECG) abnormalities. The aim of this study was to evaluate the long-term prognosis in such patients. Methods and Results: A total of 108 patients with LVA or LVD having ECG-abnormalities were assessed. The patients were classified into 2 groups according to ECG abnormalities: a distinct ECG group (8 ECG patterns known to be frequently associated with LVA/LVD); and a control group (all other ECG abnormalities). The primary endpoint was a composite of cardiac death, rhythm disturbances, syncope, embolic events, and hospitalization for cardiovascular events. Mean patient age was 64±10 years; 45 (42%) were male; median follow-up (FU) was 50 months. The primary endpoint occurred in 12/27 patients from the distinct ECG group and in 15/81 patients in the control group (44% vs. 19%; P=0.01). Cardiac event rate per year (CER) was 1.8% vs. 0.8%, respectively. There were no cardiac deaths during FU. Symptoms (arrhythmia-related symptoms, syncope, and embolic events) at time of diagnosis increased the incidence of adverse events during FU (70% vs. 28%; P=0.05; CER 2.9% vs. 1.1%). Age ≥64 years, presence of LVD, gender, and location of the anomaly did not affect the incidence of adverse events. Conclusions: The incidence of adverse events in symptomatic patients with isolated LVA or LVD and distinct abnormal ECG patterns is increased during long-term FU. None of the present patients, however, experienced cardiac death.  (Circ J 2012; 76: 2465–2470)