Doppler-echocardiography has proved useful in the assessment of mediastinal masses. We present the case of a young man with fever and new systolic murmur. Echocardiographic examination revealed a paracardiac mass compressing the right ventricular outflow tract and Doppler flow study detected marked acceleration in luminal narrowing. Complete remission of the tumour was obtained with subtotal resection and chemotherapy. Histological diagnosis was of embryonary carcinoma with areas of endodermic sinus. A new Doppler-echocardiography study showed disappearance of both the mass and the compression and showed normal right ventricular outflow tract flow.