I can't speak much to ambulatory because I am inexperienced there. However, cath lab is definitely a different world of nursing. There are certainly pros and cons to it as there are in all areas but it is definitely not for everyone. You generally receive a 3 month orientation if you are learning all 3 roles: scrubbing, monitoring, circulating. Scrubbing is the most challenging role for nurses to learn because it's 100% new skills that we are not previously trained for. It involves manual dexterity, speed, anticipation of the doctor's needs, lots of equipment to learn how to use, and working under pressure. Learning this role requires consistency with a good preceptor that likes teaching. Once I became comfortable in scrubbing, I find that this role is the most fun. Circulating will come most naturally to you as a nurse. If you are thinking about working in an interventional cath lab (as opposed to diagnostic only) you will feel most comfortable having cardiac critical care experience. Situations you will encounter involve hypotension, bradydysrhythmias, mixing and titrating vasopressor drips, right heart catheterizations and hemodynamics, chest pain, MI and cardiogenic shock patients, assisting with insertion of IABPs and transvenous pacer wires, pulling arterial sheaths, etc.
You will learn SO much about all different forms of heart disease and ACS. I feel that my experiences in cath lab have made me a much more well-rounded cardiac nurse. It's a very fast-paced environment in terms of getting the patient on the table and prepped, do the case, give report and get the patient out and the room turned around for the next case. Keeping the schedule going and getting the docs started on time can get stressful. You may enjoy not dealing with total patient care anymore and the challenges that come from having family members around all the time.
It's nice to work dayshift and be closed for elective procedures on the weekend/holidays. Depending on how much staff the lab has, you will have a certain amount of required call. Usually you have 30 minutes to return to the hospital. Carrying the pager typically gives you between $3-5/hr (which truly adds up on your paycheck!!) and time and half for callbacks. On average you may be there between 1.5-3 hours. However callbacks at 2 am and having to work the whole next day is exhausting. On the other hand, to help save someone's life in the acute STEMI situation is extremely satisfying and rewarding. Wearing lead all day can be physically tiring, so take care of your body.
Finally, I have found that the most challenging part of working in cath lab involves working with so many team members for one patient. There may be specially trained cardiovascular technicians and radiologic technologists. You no longer have the same autonomy in caring for your patient. It requires a lot of effective communication and team work. And people, as you know, can communicate very differently than you. It is hard to verbalize the culture that exists in many labs..but basically my advice would be to seek every opportunity to learn how to do all the skills even if it scares you and maintain self-confidence.
Probably this is more than you ever wanted to know, but I hope it helps you in making your decision!