We tested the impact of associative strength and retrieval heuristics in false source memory. We arranged 12-item associative lists in descending order of backward associative strength to a critical non-presented item and then split them into 6-item sub-lists at the median. High- and low-strength sub-lists were correlated with presentation source. Source claims for falsely remembered critical items were more often to the presentation source of high-strength items, which we have labeled the "source-strength effect." With only two exceptions in Experiment 2, the source-strength effect was produced even when differences in source memorability led participants to infer generally that items lacking source evidence were presented in the low-strength source. Indeed, the influence of associative strength on source attributions was shown to be completely independent of this inference strategy in a third experiment. This study demonstrates that source details of concepts most highly related to critical items are retrieved with false memories.