A resuscitation bag was stolen from inside an ambulance while it was attending a patient at an address in East Sussex, police have said.
The "first response" resuscitation bag was stolen from the South East Coast Ambulance vehicle in Green Street, Eastbourne, about 2345 GMT on Thursday.
It contained a blood pressure reader, oxygen and nebulisers, but no drugs.
"This was an extremely dangerous and irresponsible act," said ambulance service spokesman David Dixon.
"It potentially put lives at risk. The individual or individuals who did this need to know the seriousness of their actions."
Sussex Police and the ambulance service have appealed for anyone with information about the theft to come forward.