Hey! I have been working now for seven months, going on five months of being by myself. I think your feelings are totally normal. I too work on a cardiac unit, its a mixed ICU and step-down. I mostly have step-down patients, or "very light" ICU until I gain more experience to take care of sicker patients. I feel like one day I feel okay and the next I feel like I know nothing. Just today I was thinking about how I feel like I need to work on critical thinking quickly when a patient is going south. Personally, I think you're having these emotions because you deeply care about what you're doing. I think its a good thing to question your practice and know what you need to work on because it will make you a stronger nurse. I would say just keep asking questions and absorbing everything you can. I too got really interested in the OR and told myself to give it a year before I changed. I feel like now I know I am where I am supposed to be. Cardiac may not be your thing and that's okay too, I think time will help you figure that out. If you ever need to talk, I'm here for you!