The ACT government spent almost $4 million over four years on 56 cardiac monitors and, last year, defibrillators to replace models in the ambulance fleet.

But the units quickly began experiencing faults on the streets, despite two months of field testing, and three weeks of demonstration in staff training. The government says the problems did not pose a risk to patients, and paramedics worked around the faults. The revelations prompted the Canberra Liberals to ask a series of questions of the government in October last year, in an attempt to gauge the scale of the problem.

The response to those questions shows there were 16 transmission issues, including 10 problems with crucial bluetooth connections between the cardiac equipment and mobile phones that transmit information to electrocardiograph units.

There were 18 issues with inaccurate blood pressure readings, and one problem with a battery not charging properly.

Opposition emergency services spokesman Brendan Smyth called on the government to give assurances that no problems had been experienced since December.

''It's taken a long time for the full extent of the problem with these defibrillators to become public, and it's only through our questioning in the assembly that we do now have some numbers.''

But Emergency Services Minister Simon Corbell and ACT Ambulance Service chief officer David Foot said the issues had been resolved.

There has only been three real technical problems since December, two of those caused by unrelated physical damage to the units.

"The technical problems associated with the ACT Ambulance Service's new cardiac monitors last year were fixed with the assistance of the supplier,'' Mr Corbell said. Mr Foot said the supplier flew in staff to help, and provided ''fantastic'' support, including major software updates.