This is very difficult for me to answer because I live in the UK and over here it depends on the trust running the
hospital. It varies. However, I do know that a cardiologist will be on call and they
stay in the hospital over night, sleeping in any available room. The hospitals which have a cardiac ward are strict on this. Usually it will not be a consultant cardiologist, but they are in the hospital for many hours every day, early hours until late evening.