The findings of past research using d-tubocurarine chloride as a control procedure in heart rate conditioning have been equivocal. The present experiment compared classical heart rate conditioning under neuromuscular blockade by d-tubocurarine chloride, and a pharmacologically more specific blocker, carbolonium bromide. Both groups were compared to a placebo condition. The results indicated that carbolonium bromide and placebo treated animals acquired deceleratory cardiac conditional responses, but animals treated with d-tubocurarine chloride did not. Unconditional acceleratory responses were found in groups. The findings were discussed in relation to classical conditioning and the psychopharmacology of neuromuscular blockade.