As animals (or people) get older, the internal organs tend to decrease in efficiency (e.g. the heart, lungs, kidney, and liver), even if they are still bright and cheerful. Anaesthesia places a strain on these organs too. It is often important to know how well the organs are working before anaesthesia, and so we sometimes recommend some tests (e.g. blood samples) first. Once we know about the organ function, we can design an appropriate anaesthetic for an older animal. It will have more risk than in a young, healthy dog, but by using careful preparation and monitoring during and after anaesthesia we successfully anaesthetise large numbers of older dogs.