['Heat stress prior to induction of various forms of cardiac injury has been shown to result in preconditioning and attenuation of subsequent damage. We evaluated the effects of whole-body hyperthermia (WBH) on experimental autoimmune myocarditis (EAM) induced either by injection of myosin or by adoptive transfer of lymphocytes.', 'Lewis rats were pretreated with WBH either 24 h prior to EAM induction (Group A1) or 14 days following EAM induction (Group A2). The control group included myocarditic rats that were not exposed to WBH (Group A3). Rats from Group A1 exhibited significant protection from myocarditis as compared to rats from Group A3, evidenced by reduced myocarditis scores (1.60+/-0.96 vs. 2.88+/-0.35, P=.016). Rats from Group A2 also exhibited protection from myocarditis although not significantly. In a second experiment, we used adoptive transfer of myosin-reactive lymphocytes to study the mechanism of WBH effect on myocarditis. There was evidence of microscopic myocarditis in four out of five rats that were injected with active lymphocytes (the Control Group B3). Myocarditis was not observed in rats adoptively transferred with preheated rat lymphocyes (Group B1) nor in preheated rats, which underwent administration of nonheated rat lymphocyes (Group B2).'] Does whole-body hyperthermia attenuate experimental autoimmune myocarditis in the rat?