Objective: To evaluate whether ultrafine particulates (UFPs) have direct deleterious effects on cardiac function through activating MAPK signaling. Methods: Langendorff-perfused Sprague-Dawley rat hearts were randomly divided into 2 groups (n=10/each group). In control group, the rat hearts were perfused with Tyrode’s buffer for 40 min; in UFPs-treated group, the hearts were perfused with UFPs at a concentration of 12.5 mg/L. Cardiac function was determined by measuring left ventricular developed pressure (LVDP), left ventricular peak rate of contraction and relaxation (±dp/dt_max) and coronary flow (CF). The levels of malondialdehyde (MDA), superoxide dismutase (SOD), total anti-oxidant capacity (TAOC) were detected in order to evaluate cardiac oxidative stress via the thiobarbituric acid assay, water soluble tetrazolium salt assay and colorimetry, respectively. The expressions of p-p38 MAPK, p-ERKs and p-JNKs in the myocardium were observed using immunohistochemical staining and Western blots. Results: No significant changes in cardiac function were detected before and after the perfusion in control group while UFPs perfused hearts showed a decline in cardiac function in a time-dependent manner (all P<0.05). In UFPs-treated group, LVDP, +dp/dt_max, -dp/dt_max and CF were statistically reduced from (82.6±2.1) mmHg, (1 624±113) mmHg/s, (1 565±116) mmHg/s, (12.0±0.2) mL/min to (56.8±4.4) mmHg, (1 066±177) mmHg/s, (1 082±134) mmHg/s, (8.7±0.3) mL/min (all P<0.05), respectively. Furthermore, The comparison between the two groups observed that UFPs perfusion caused a significant decrease in cardiac function at 30 and 40 min compared with the control group (all P<0.05). At the end of the perfusion, the level of MDA was increased from (0.98±0.14) nmol/L to (1.95±0.18) nmol/L, while SOD and TAOC were reduced from (12.50±1.87) U/mL and (6.83±1.16) U/mL to (6.50 ±1.04) U/mL and (3.67±0.82) U/mL (all P<0.001) in UFPs group, respectively. In coincidence with these changes, immunohistochemistry and Western blots results showed that the levels of p-p38 MAPK, p-ERKs and p-JNKs in the myocardium significantly increased in UFPs group as compared with control group (all P<0.05). Conclusion: The results of this study demonstrated that the short-term exposure of UFPs to the isolated rat hearts has direct and acute toxic effects on cardiac function, probably related to attenuation of anti-oxidative capacity and activation of MAPK signaling pathways.