Nitric oxide (NO) produced by myocardial nitric oxide synthase has been implicated as a modulator of myocardial contraction [correction of contracion]. This paper reviewed the reports on myocardial contraction modulated by NO, its mechanism, and regulation of expression and activity of iNOS. NO was recently shown to produce biphasic contractile [correction of contratile] effects on myocardium: augmentation at low levels and depression at high levels. The up-regulation of inducible nitric oxide synthase (iNOS) often negatively modulates myocardial function.