Effects of physostigmine salicylate (PH; 0.1 mg/kg i.p.), prostigmine bromide (PR; 0.1 mg/kg i.p.) and/or atropine sulfate (AT; 1.0 mg/kg i.p.) on isoprenaline (ISP; 30 mg/kg s.c.)-induced 45Ca uptake and Pi content of the heart and on cardiac and hepatic glycogenolysis were studied in albino rats. PH or PR markedly inhibited ISP-raided cardiac Ca2+ uptake and Pi content, and cardiac and hepatic glycogenolysis, while AT had no such action. These inhibitory actions of PH were blocked by AT. PH, PR or AT per se had no action on any of these parameters. It appears that anticholinesterase agents can antagonize some of the injurious effects of isoprenaline on heart, the action being mediated through muscarinic receptors.