Clinical and experimental studies have shown that trauma combined with hemorrhage shock (T/HS) is associated with myocardial contractile dysfunction. However, the initial events triggering the cardiac dysfunction are not fully elucidated. Thus, we tested the hypothesis that factors carried in intestinal (mesenteric) lymph contribute to negative inotropic effects in rats subjected to a laparotomy (T) plus hemorrhagic shock (HS; mean arterial blood pressure of 30-35 mm Hg for 90 min) using a Langendorff isolated heart preparation. Left ventricular (LV) function was assessed 24 hrs after trauma plus sham shock (T/SS) or T/HS by the LV developed pressure (LVDP) and the maximal rate of LVDP rise and fall ±dP/dt_max) in five groups of rats; 1) naïve un-instrumented and rats subjected to 2) T/SS, 3) T/HS, 4) T/SS with mesenteric lymph duct ligation (LDL) or 5) T/HS+LDL. Cardiac function was comparable in hearts from naïve, T/SS and T/SS+LDL rats. Both LVDP and ±dP/dt_max were significantly depressed after T/HS. The T/HS hearts also manifested a blunted responsiveness to increases in coronary flow rates and Ca²⁺, and this was prevented by LDL prior to T/HS. Although electrocardiograms were normal under physiological conditions, when the T/HS hearts were perfused with low Ca²⁺ levels (0.5 mM), prolonged P-R intervals and second-degree plus Wenckebach-type atrioventricular blocks were observed. No such changes occurred in the control or T/HS+LDL hearts. The effects of T/HS were similar to the Ca²⁺ channel antagonist, diltiazem, indicating that an impairment of cellular Ca²⁺ handling contributes to T/HS-induced cardiac dysfunction. In conclusion, gut-derived factors carried in mesenteric lymph are responsible for acute T/HS-induced cardiac dysfunction