Data from the tropical Pacific Ocean for the period 1980--2002 are used to examine the persistence of sea surface temperature (SST) and upper ocean heat content variations in relation to El Ni¿o and the Southern Oscillation (ENSO). The present study demonstrates that, unlike for SST, there is no spring persistence barrier when considering upper ocean heat content. Conversely, there is a persistence barrier for heat content in boreal winter related to a seasonal reduction in variance. These results are consistent with ENSO forecast model studies indicating that accurate initialization of upper ocean heat content often reduces the prominence of the spring prediction barrier for SST. They also suggest that initialization of upper ocean heat content variations may lead to seasonally varying enhancements of forecast skill, with the most pronounced enhancements for forecasts starting early and late in the development of ENSO events.