We describe the case of a dual chamber rate responsive pacemaker (Relay, mo
del 294-03, Intermedics,Angleton,TX, USA) implanted in a 68-year-old male f
or sick sinus syndrome, which was not working properly when programmed in t
he DDIR mode, th us determining occasionally a sort of "VVI" pacing. Howeve
r, the pacemaker performed well when programmed in the DDDR mode. We discov
ered that this was not a malfunction of a single device but rather a genera
l behavior of this family of Intermedics dual chamber pacemakers (also not
rate responsive), caused by a software problem.