I'll start off by saying that I am careless with Stethoscopes, which is how I ended up writing this review in the first place. Intubation? Lost stethoscope. Central line? Lost stethoscope. Five minutes for lunch? Probably microwaved my stethoscope. The life of an ER resident is crazy, surreal, and amazing. It is also provides the optimal conditions for evaluating stethoscopes. Maybe you're starting medical/nursing school and this is your first big purchase, or maybe you're a veteran at the game and this will be the last of your career. Either way, this is a worthy upgrade to the Cardiology III, and maybe even the Master cardiology.First, i'll start with the similarities. I've owned all three and the acoustics are going to be a dramatic step up from a cheaper brand or model. So now that we're in the 'top tier' with these three, the differences at the top are going to be more subtle.As far as acoustics, Cardiology IV and Master Cardiology are comparable. Anecdotally, I find the Cardiology IV is better at isolating background noise. You will easily pick up any grade 2/6 murmur with either of these models (A guess a better question might be, does it matter?). The cardiology III lags just a bit behind. To a novice med or nursing student, the differences will not be appreciable. But for those who have trained on a lower quality product, you will be pleased with the upgrade.Tubing: The Master Cardiology and Cardiology III both have your standard rubber tubing. The cardiology IV is equipped with a noticeably thicker (and stiffer) synthetic. What this translates to practically is a more comfortable position on your neck (It stays put). I much prefer the new tubing, although time will tell with durability.Size/weight: Master cardiology is the heaviest, with a large diaphragm that will make you feel like a giant on your pediatrics rotation. It also feels to be the most solidly built. Next is the Cardiology IV, which on my kitchen scale weighed 7 grams more than my cardiology III. Practically, it feels to be a similar weight and diaphragm is a similar size. However, the build quality is a huge step up from the Cardiology III. This thing feels solid and is a pleasure to hold.Other features: The tunable diaphragm on the Cardiology IV is top notch. It allows the small diaphragm to be utilized strictly for smaller humans, which is perfect for many fields.Warranty: Who cares? You'll lose all three before you replace one.Colors: I went for standard black on my Cardio III as it was my first stethoscope and i wanted to be professional in my selection. I purchased the Cardiology IV in Hunter Green and could not be happier with that decision. It is elegant and professional, but also different enough that it allows quick identification. I honestly would encourage going against the grain and selecting an actual color. It will bring you joy during those long days and also serves a subtle kick in the butt to the hierarchy and pretentiousness of medicine (At least in my own head).In short, I would highly recommend the Cardiology IV over the others. While the Master Cardiology may have the best acoustics (Debatable), it is clunky and impractical if you have to see kids. It is also noticeably heavier and will likely end up off your neck. There is simply no reason to buy a Cardiology III anymore unless you buy it at steep discount (I'd still probably spend the additional cash on the better model). I coincidentally found my Cardiology III a few days ago and briefly considered returning the Cardio IV, but I just couldn't bring myself to do it (I don't know if i'd recommend as an upgrade unless you are ready for a new stethoscope). At least I'll have a spare :)Left is Cardiology III in black, right is Cardiology IV in Hunter Green, 27 inch. Master Cardiology is probably in a refrigerator somewhere.