PROJECT SUMMARY/ABSTRACT Optimal management of patients with mitral regurgitation (MR) involves accurate grading for the disease timely intervention, proper follow-up, and patient-specific therapeutic decision-making. A recent study in France showed that although MR was clearly identified and coded in the patients' discharge summary, only less than 10% of those admitted with significant MR underwent a valve intervention within 1 year. This leaves a vast majority of the patients untreated. They found that the rate of mitral valve intervention was significantly low for both primary and secondary MR. This high level of undertreatment is even more striking considering that all individuals were inpatients, admitted to French hospitals with relatively easy access to cardiologists. Alternatively, a significant and unfortunate outcome of inaccurate grading of MR severity is over-treatment of the patients whose grade of valve regurgitation has been erroneously reported. Every so often patients undergo unnecessary corrective procedures due to misgrading their MR. The under- or over-treatment is a significant and unfortunate outcome of inaccurate grading of MR severity. Volumetric Echo-PIV visualizes and quantifies 3D blood flow velocity field from echocardiographic data based on the governing equations of the flow. Given the ubiquitous availability of the echocardiography systems, V- Echo-PIV is inexpensive, accurate, and accessible. Funded by 1 R01 HL153724-01A1, we are currently studying the feasibility of V-Echo-PIV as a tool to assess right ventricular (RV) flow for diagnosis and follow up of patients with pulmonary hypertension (PH). These patients require frequent monitoring, often including repeated invasive right heart catheterization (RHC) due to their clinical status, which has led to a significant healthcare burden. Noninvasively derived RV hemodynamics indices from V-Echo-PIV that correlate with PH patients' clinical condition could significantly reduce the cost and morbidity of the current invasive tests. Based on our recent success in characterizing the RV blood flow in the PH patients and healthy control subjects, this supplement award seeks to study the feasibility of V-Echo-PIV to quantify MR and thus eliminate intra- and inter-operator variability in grading MR. V-Echo-PIV utilizes matrix array ultrasound transducers of current standard echocardiography systems and requires only a few heartbeats (up to 4) to process and obtain the blood flow's 3D velocity vector field in the heart chambers. We hypothesize that by measuring the 3D velocity field in the left ventricle and left atrium via V-Echo-PIV, it is possible to characterize the flow conversion zone in 3D and accurately grade MR. To achieve the proposed research objectives, the following specific aims are set to be accomplished in a 1-year duration of the project: SPECIFIC AIM 1: Devise a protocol for high-speed contrast 3D echocardiography to image the flow in the left heart to charac...