Currently, autologous peripheral stem cell transplantation used as a therapeutic modality in the treatment of various hematological malignancies is gaining more popularity day by day. In this method, the patient's own peripheral stem cells are collected by a proper method and stored at -80 degrees C until they are reinfused into the patient after being rewarmed in water bath at 37 degrees C. A number of complications have been reported related to reinfusion of the cryopreserved cells into the patient. These may include noncardiovascular complications such as nausea, vomiting, flushing, abdominal pain, chest discomfort, and headache, as well as cardiovascular complications like arrhythmias, hypotension, and hypertension. Hypothermia related to rapid infusion has been reported as the main factor underlying the cardiovascular complications. Electrocardiographic findings of hypothermia include sinusal bradycardia, prolonged QT and PR intervals, widened QRS complexes, and J wave, which is a ECG abnormality characterized by supraventricular and ventricular arrhythmias. We here present two cases of giant J wave caused by hypothermia during infusion of cryopreserved autologous peripheral stem cell that is detected by ECG and regressed after infusion ceased.