Djungarian or Siberian hamsters (Phodopus sungorus) acclimated to short photoperiod display episodes of spontaneous daily torpor with metabolic rate depressed by ~70% and body temperature reduced by ~20°C. To study the cardiovascular adjustment to daily torpor in Phodopus, electrocardiogram (ECG) and body temperature (T_b) were continuously recorded by telemetry during entrance into torpor, in deep torpor, and during arousal from torpor. Minimum T_b during torpor bouts was ~21°C and heart rate, ~349 bpm at euthermy, displayed marked sinus bradyarrhythmia at ~70 bpm. Arousal was typically completed within ~40 min followed by a sustained post-torpor inactivity tachycardia (~540 bpm). Absence of episodes of conduction block, tachyarrhythmia or other forms of ectopy throughout the torpor cycle demonstrates a remarkable resistance to arrhythmogenesis. The ECG morphology lacks a distinct isoelectric interval following the QRS complex, and the ST segment resembles the ECG pattern in mice with a prominent fast transient outward (I_to,f) K⁺ current determining the early phase of ventricular repolarization. During low-temperature torpor, the amplitudes of the QRS complex substantially increased suggesting that, in the euthermic state, the terminal portion of ventricular depolarization is fused with the beginning of repolarization, low T_b acting to decorrelate the superposition between depolarization and repolarization by delaying the repolarization onset. Atrio-ventricular and ventricular conduction times were prolonged as function of T_b. In contrast, the QT vs. T_b relationship showed marked hysteresis indicating the operation of nonlinear control mechanisms whereby the rapid QT shortening during arousal results from additional mechanisms (probably sympathetic stimulation) other than temperature alone.