Patients after open heart surgery are often at risk for developing blood clots and stroke, especially after heart valve surgery or in those who develop an irregular heart rhythm called post-operative atrial fibrillation (POAF), which can occur in up to 1 in 4 patients. Blood thinners are used to lower the risk of stroke, hospitalization and death, but blood thinners are not well-studied after open heart surgery. My research program will aim to determine the safest and most efficacious blood thinner regimens after open heart surgery in those with POAF and after certain types of valve surgery. The main research question is to determine if a new class of more convenient blood thinners called non-vitamin K oral anticoagulants are just as safe as the gold-standard warfarin early after open heart surgery. We are currently successfully running a pilot study to gather data for the design of a larger trial to help us answer this question. For patients after valve surgery, including novel trans-catheter valve procedures or surgical mitral valve repair, we are conducting a thorough review of the existing published studies prior to designing appropriate follow up studies that may use registry or database information to collect outcomes.