What's seen when stress echocardiography shows ischaemia? Can this happen without angina?
A number of things can be seen. Ischaemia is typically caused by the narrowing of blood vessels that prevents perfusion (blood flow) to the heart or other organs. When the heart muscle doesn't get enough oxygen, the walls of the heart might not "beat" (i.e. contract) properly. We observe this and thus can tell if a coronary artery is reduced or blocked or fine. It doesn't give absolute numbers of how blocked it is, although observation of the way the muscle moves can give some indication. Contrast can further allow us to visualise the wall with more detail, giving a clearer indication of coronary artery disease in the vessels that supply this part of the heart. 

Pain is caused when the heart muscle is really suffering, which doesn't occur unless the vessels are seriously blocked. They're so great that even if about 70% of the artery is blocked there is almost no effect including chest pain. In fact it is silent, which is quite worrying also. However, when the heart is most stressed, we can potentially detect decrease in perfusion from small changes in the contraction of the heart.