What fraction of the original heat flow would a 238Pu-powered device be producing?

Heat released from the first-order, radioactive decay of plutonium-238 (238Pu) has been proposed as a steady source of heat energy for long-term applications. The half-life of 238Pu is 86 years. What fraction of the original heat flow would a 238Pu-powered device be producing when it is retrieved from a remote location 43 years after deployment?