I've had them in the veins going up my neck, usually just for a short time, and usually during a bout of tachycardia.
When I got them worse, and continuously, I went to Urgent Care, and they sent me, by ambulance, across the street to the hospital because my rhythm was messed up.
I don't want to sound alarmist, but I suggest that you call your cardiologist and describe the symptoms. The doctor may have you come in for an EKG. In my case, I would get these bouts of SVTs every few weeks, and they'd last for a few minutes - I never got 'used' to them, but I've been having them off and on for more than 40 years, and they always resolved in a few minutes -- until the last time it happened.
Again - with a bovine valve, I would call my cardio and describe the symptom This is something that I would NOT screw around with - especially if this has lasted for a while.