I had my mitral valve replaced with bovine valve in November 2018. I have had a variable heart rate ever since. My cardiologist has me on blood thinner and says my HRV is ok as long as I don't get any bad symptoms like shortness of breath, pain etc.. The condition at times is like border line Afib. I have seen a 2nd cardiologist and he agrees with the previous. Being more active seems to help but I am aware of the variation in beat especially at bed time. When I take my EKG with Kardia mobile, it always indicates possible Afib.