Are some Pacemakers better than others? My previous PM was a Medtronic VIVA XT Defib item that was replaced with a Medtronic Claria MRI CRT-D this past Nov 30. The Claria looks to be around 20% smaller than the VIVA XT. Two weeks prior, I took a pulmonary treadmill stress test - Performing it was a breeze. Today, I couldn't perform that chore. Either the new PM isn't as effective as the old, or the series of ills I suffered in late Dec/early Jan took their toll. (diverticulitis then C-Diff followed by a pneumonia that landed me in the hosp. for a few days.) Can one go downhill that quickly? A positive note: That Holter around my neck comes off in 2 hours!!