Functional mitral regurgitation (FMR) is relatively common in heart failure and it is associated with adverse prognosis. The severity of FMR is usually assessed by echocardiography. Tissue Doppler echocardiography is used to acquire signals to determine the myocardial systolic functional parameters, including systolic ejection velocity and the systolic isovolumic acceleration (IVAs) rate. We investigated the utility of isovolumic acceleration parameters to grade the severity of FMR in nonischemic dilated cardiomyopathy (DC) patients. We analyzed the left ventricular systolic IVA rate, systolic isovolumic contraction (IVCs) velocity, and IVA duration (IVAd) values in 73 patients with DC. Patients were subgrouped according to FMR grade (Group I = mitral regurgitation mild and moderate; Group II = mitral regurgitation severe). IVAs was similar between two groups; however IVCs and IVAd were significantly higher in Group II than Group I. The IVCs cutoff value to predict severe FMR was 1.2 cm/sec (sensitivity 75% and specificity 70%). The IVAd cutoff value to predict severe FMR was 33 ms (sensitivity 77% and specificity 77%). Patients with IVCs >= 1.2 cm/sec and IVAd >= 33 ms had significantly higher FMR volume than the other subgroups. IVCs and IVAd values are useful to determine FMR severity in patients with DC. (Echocardiography 2010;27:815-822).