SUMMARY
Sinus tachycardia is common in pediatric age, and is usually related to benign physiological conditions, such as somatoform disorders. Nevertheless, it can also be a presenting sign of a disease with an ominous prognosis. We present a case of a previously healthy 15-year-old girl, admitted for syncope. She had been well until one week before admission, when thoracic pain developed. One month prior to the admission she had started oral contraceptives. On examination, she had persistent sinus tachycardia, despite hemodynamic stability and no other associated sign or symptom. Thoracic computed tomography angiography revealed thrombi in the main pulmonary arteries, which confirmed bilateral pulmonary embolism. She was started on anticoagulation with unremarkable clinical course evolution. Pediatric pulmonary embolism is rare, although probably underdiagnosed, given the nonspecific presentation in most cases. Maintaining a high level of clinical suspicion of pulmonary embolism avoids delay in the diagnosis, allows early appropriate treatment and improves prognosis.