Four-year-old male, previously healthy, with no trauma report, referred to paediatric cardiology evaluation for retrosternal chest pain and fatigue. Clinically, a systolic murmur grade III/VI was heard at the mitral focus. The chest X-ray showed cardiomegaly with enlarged left-side cavities (Fig 1) and the transthoracic echocardiogram showed a globular appearance of both left chambers with a single subvalvular mitral aneurysm, moderate mitral regurgitation and flow arising from the left ventricle into the aneurysm (Fig 2). Cardiac function was globally preserved and the haemodynamic status was stable. The patient was kept in the intensive care unit for close monitorisation. An urgent cardiac computed tomography was requested for more accurate anatomic documentation and surgical approach planning, but not performed - after 3 hours after admission the patient suffered sudden clinical deterioration with ventricular tachycardia and severe haemodynamic compromise which rapidly progressed to cardiorespiratory arrest, non-reversible with the resuscitation procedures. Subvalvular mitral aneurysm is a potentially fatal and rare condition.^{Reference Vinitha Viswambharan, Rajat, Rajiv and Airan1} Numerous causes are suggested, such as inflammatory, infectious, or traumatic. The occurrence of non-infectious and non-traumatic aneurysms supports that mitral subvalvular aneurysms can result from a congenital defect of the valvular ring.^{Reference Ribeiro, Mendes, Vicente, Menardi and Evora2} Clinical presentation relates to congestive heart failure signs, chest pain, heart murmur and may be associated with cardiac arrhythmia phenomena. Treatment is surgical, the aneurysm neck is closed with mitral valve repair or prosthesis implantation if associated mitral dysfunction is documented.^{Reference Ribeiro, Mendes, Vicente, Menardi and Evora2,Reference Sarioglu, Turkekul, Arnaz, Sisli, Yalcinbas and Sarioglu3}

Figure 1. Chest radiograph; anteroposterior projection demonstrating cardiomegaly.

Figure 2. Doppler transthoracic echocardiogram, apical four-chamber view, demonstrating mitral regurgitation jet (MR), left atrium (LA), right atrium (RA), right ventricle (RV), left ventricle (LV), subvalvular mitral aneurysm (AN).