We herein report the case of a 23-year-old man who presented with recurrent pancreatitis and was diagnosed with primary pancreatic extranodal natural killer/T-cell lymphoma, nasal type, involving the right ventricle. The cardiac involvement was screened and confirmed by transthoracic echocardiography (TTE), cardiac magnetic resonance imaging and fluorodeoxyglucose positron emission tomography. Although the patient did not have any cardiac symptoms or evidence of arrhythmia before chemotherapy, he presented with fatal newly developed ventricular tachycardia during the early stages of chemotherapy. The follow-up TTE after his chemotherapy demonstrated markedly decreased thickness of the invaded myocardium, thus suggesting that the myocardium infiltrated by lymphoma cells might become vulnerable to fatal arrhythmia with tumor regression.