Lack of evidence for ventricular arrhythmias and QT interval prolongation after UCB-MNCs transplantation. Multiple doses (0.2, 0.4 and 0.8 million cells) of UCB-MNCs were transplanted on the right ventricle to evaluate cardiac safety and tolerability (n = 7). (A, B) Body weights and temperatures measured up to three weeks followed by UCB-MNCs transplantation. Heart rate (HR) was derived from telemetric recording in conscious animals (C). Data presented as means ± SE. (D) ECG tracing from a conscious mouse implanted subcutaneously with a telemetry transmitter recorded at baseline and 3, 6, 9, 12, 15, 18 and 21 days after intramyocardial injection of UCB-MNCs. UCB-MNCs, umbilical cord blood-mononuclear cells.