We have previously reported that diesel exhaust particles (DEP) caused a negative inotropic effect that was followed by cardiac arrest in the isolated atrial preparation of guinea pigs. The purpose of this study was to examine the systemic effects of DEP on electrocardiographic (ECG) changes using guinea-pigs. We found that intravenously administered dimethyl sulfoxide (DMSO) extract of DEP solution induced arrhythmias and deaths via complete atrioventricular (AV) block in guinea pigs. The LD of DEP solution was 132.0 +/- 7.2 mg/kg. The coefficient of variance (CV) of LD measured by the modified Hatcher-Magnus method was relatively small (5.5%). Fractions of DEP extracted by hexane, ethanol or methanol, 4-hydroxyphthalic acid 2-methyl ester, a compound isolated from methanol extract of DEP did not induce significant ECG changes in guinea pigs. As compared with fresh DEP solution, the DMSO/DEP solution used in the present study induced similar cardiac toxicity after being stored in a freezer at 4 degrees C for 3 days. These results suggest that stable and water-soluble fractions of DEP may be responsible for cardiotoxicity.