Angiotensin-converting enzyme inhibitors (ACEi) protect the heart against ischemia/reperfusion injury. Part of this cardioprotective effect may be mediated through kinins. Because kinins are also metabolized by neutral endopeptidase (NEP) 24.11 in vivo, we hypothesized that (a) inhibition of NEP-24.11 would afford cardioprotection similar to that of ACEi and potentiate the effect of ACEi; and (b) these effects are mediated by kinins or atrial natriuretic peptide (ANP) or both. In Lewis inbred rats, the left anterior descending coronary artery (LAD) was occluded for 30 min, followed by 120-min reperfusion. Immediately before reperfusion rats received vehicle, the ACEi ramiprilat, the NEP-24.11 inhibitor (NEPi) CGS24592, or both. To test whether the effect of NEPi could be suppressed by blocking kinins or ANP, the kinin-receptor antagonist icatibant or ANP antagonist HS-142-1 was administered before LAD occlusion. In controls, infarct size/risk area was 69 +/- 4%; NEPi reduced this to 24 +/- 4% (p < 0.001) and ramiprilat to 20 +/- 3% (P < 0.001). NEPi did not potentiate the effect of ramiprilat (infarct size/risk area, 18 +/- 4%). The protective effect of NEPi was blocked by icatibant; infarct size/risk area, 61 +/-4%, significantly larger than NEPi along (p < 0.001) but no different from controls. The effect of NEPi was slightly diminished by the ANP antagonist HS-142-1 (infarct size/risk area, 35 +/- 3%; NS vs. NEPi alone). Thus NEP-24.11 participates in catabolism of kinins in the heart; inhibition of NEP-24.11 may increases cardiac kinins, which are responsible for the cardioprotective effect of NEPi.