The men were taking part in the 13.1-mile (21km) city centre event when they collapsed within minutes of each other close to the finish line.
The East of England Ambulance Service said crews helped a man in his 40s in Victoria Avenue at 11:45 GMT.
Nine minutes later, a man thought to be in his 30s collapsed. Both were taken to Addenbrooke's Hospital.
An ambulance spokesman said crews resuscitated both men and were able to get a heartbeat at the scene.
An off-duty paramedic competing in the half marathon also stopped to help one of the men and travelled in the ambulance to hospital, he said.
Seven-thousand runners took part in the fifth Cambridge Half Marathon, which finished near Jesus Green.
Two runners are in a critical condition after suffering cardiac arrests at the Cambridge Half Marathon.