The success of heart transplantation is limited by the negative correlation between the length of the cold ischemic storage period and the quality of functional recovery. We use 23Na, 31P NMR spectroscopy, and hemodynamic parameters to describe temperature‐dependent changes in sodium influx and the concentration of phosphorus high‐energy compounds during different storage periods. Perfusion with Krebs—Henseleit solutions containing Dy(TTHA)3‐ permitted discrimination of intra‐ and extracellular sodium during cold ischemic storage. The 23Na NMR visibilities under the acquisition and processing parameters used in our experiments were 40 ± 4% for the intracellular compartment and 97 ± 11% for the extracellular compartment. At 4°C, the intracellular Na+ accumulation exceeded that observed at 15 and 22°C. The ATP and PCr depletion rates were much lower at 4°C and the left ventricular contractility was higher after longer periods of storage, as the storage temperature decreased. The intracellular Na+ concentration cannot serve as a marker for the postischemic recovery probability. The relative activity of the Na/K ATPase pumps is not correlated with the preservation success. However, intracellular sodium ion accumulation is a major factor in the time lag of the reperfusion recovery.© 1992 Academic Press,Inc.