Objective: To evaluate the role of transoesophageal echocardiography and problems related to safety during the surgical repair of congenital cardiac malformations in children. Methods: We examined the transoesophageal recordings made in 350 children with congenital cardiac diseases, aged from 2 months to 17 years and 9 months, with a median age of 2.7 years, tracings having been taken both before and after cardiopulmonary bypass. All patients had been scanned by transthoracic echocardiography before the operative procedures. Results: Preoperative transoesophageal echocardiography added additional findings, or changed the diagnoses made using transthoracic echocardiography, in 33 cases (9.4%), among which the findings had therapeutic significance in 23 cases (6.6%) that altered the planned surgical procedures. Residual problems or sequels were detected by postoperative transoesophageal echocardiography in 57 cases (16.3%), with 13 patients (3.7%) requiring instant intervention or return to bypass for modifications of the surgical procedures. We encountered no severe complications due to the performance of transoesophageal echocardiography. Mild complications occurred in only 2 patients (0.6%). Conclusions: Transoesophageal echocardiography is a useful tool with which to determine the strategies for treatment in the perioperative period, and to improve the quality of surgical procedures in children with congenital cardiac diseases. Complications were few, but still deserved careful attention to detail.