Pulmonary embolism (PE) is a clinical entity with a high mortality rate and hence requires accurate, urgent diagnosis and emergency therapy. We report a case of successful treatment of PE in a patient with renal cell carcinoma (RCC) with tumor thrombosis of the renal vein and the inferior vena cava (IVC). PE was diagnosed using electrocardiography (ECG), echocardiography, D-dimer level elevation and contrast-enhanced computed tomography. First, ECG showed a new sinus tachycardia and T wave flattening in the inferior leads (II, III, aVf) in contrast to routine ECG performed previously at a medical health checkup. Second, echocardiography revealed a dilated right ventricle, tricuspid regurgitation, and elevation of systolic pulmonary artery pressure. We emergently inserted a temporary IVC filter at the proximal end of the tumor thrombus under serial echocardiographic evaluation, followed by thrombolytic therapy and anticoagulation therapy. After 3 days, we performed radical nephrectomy and thrombectomy of the IVC. After surgery, the temporary IVC filter was removed, and the anticoagulation therapy was continued. The patient remained symptom free 3 years after surgery. For the diagnosis of PE, it is important to compare the previous ECG obtained on routine medical health checkup and the ECG results at diagnosis. In conclusion, during a medical health checkup in clinical practice, despite its rare occurrence, a life-threatening PE should be ruled out in a patient with risk factors, symptoms, and ECG findings such as tachycardia and ST-T change in the inferior leads and patients with such findings should be urgently referred to a cardiovascular specialist.