When Tetralogy of Fallot is left untreated, symptoms of heart failure may emerge due to right ventricular dysfunction. Patients may experience a progressive increase in cyanosis (bluish discoloration). Complications related to cyanosis, such as arrhythmias (heart rhythm disorders), can also be observed. Delayed treatment negatively impacts surgical success rates and post-operative survival. For classic Tetralogy of Fallot, the optimal age for surgical intervention is typically around one year.