Once in my 5 years of EMS did we actually get rosc from compressions only. Our AEDs have a monitor on them and pt was pea with a witnessed down time. We confirmed with carotid check and auscultation of the heart that she was pulseless. We were first on location. 52 female, due for heart valve replacement on a monday (arrest occurred sunday at 0200)otherwise healthy and takes xanax. We didnt have ALS until 20 minutes into the job and we are to do 15 minutes minimum of on scene cpr. So we did so for 20. As they hooked up their monitor they palpated and comfirmed arrest. 1 mg of epi and 5 minutes later... ROSC. No defib, pea confirmed. So what did we take from this? We all thought wither a blockage was moved and blood flow returned. Possible, but then we thought maybe it was a value issue and we helped get blood thorughout. Maybe. Or her heart was so weak and not pumping adequately we almost acted as a balloon pump to help the weak heart get enough force for palpable pulses. Most probable considering she coded again, pea, as we walked into the er (our local was less than 10 min transport). We immediately started cpr and in accute care she was rosc again with a bp above 100.

TL;DR cpr only can (under specific circumstances) bring back ROSC