The donor animals are heparinized and hearts are cannulated before connecting to the Langendorff perfusion system. Before connection, the hearts are well-decompressed, so the hearts are pretty soft, i don't see any evidence of left ventricle distension. Once the perfusion started, the whole heart (both left and right) is becoming stiff. I use the constant pressure perfusion mode, so the flow rate is deceasing which is a indicator of increasing inner resistance, specifically, higher resistance in coronary system.

I try to press the heart to force the perfusate flows out, the stiff heart becomes soft again. But after a few minutes, the heart is re-stiff again. So i have to press the heart again and again. i think it the problem of right heart pressure bulidup and perfusate aggregation, however i don't know what happened to the heart and how to avoid it.