If you are interested in an academic IM residency, then having some research or presentations help since your fellow applicants (e.g., MD students) will also have those in addition to good board scores. Remember, a lot of MD students are at large research universities where they have plenty of opportunities to get bench research, or even clinical research (since these universities have attached large teaching hospitals where the attendings are doing either bench research, clinical research, or QA/QI projects) as well as residencies where residents could also use an eager medical student to help with the grunt work (in exchange for having your name on the poster/publications). Most DO schools don't have readily access to those resources (esp the newer ones with barely any clinical affiliation, no strong academic affiliation, and not near any medical research hub/centers)
Another thing to keep in mind - Cardiology participates in the Summer Match - which means application (ERAS) opens up in July (end of 2nd year of residency). So while you have 2 years to get your applications in order ... you really don't. It takes time to get IRB approval (if starting a fresh project), time to collect data, or review data. It takes time to submit for publications, wait for feedback, make changes, wait for more feedback, until it gets accepted. And poster presentations at conferences (whether regional or national ACP, ACC, etc) only occurs once a year. And this is on top of your clinical duties as an intern (and junior resident), putting in 80+ hrs/week on wards/ICU/cardiology, etc (and create a strong impression to get those strong LORs for fellowship)
That's why some take a chief year - in addition to the prestige, it also gives more time to polish one's resume.
Audition rotations outside your home institution during residency is also very difficult (and limited, subject to your residency scheduling and approval of your PD). If you are doing it in a different state, there's state licensing issues. There's medical malpractice insurance to also deal with (will your home institution cover you?). And you don't have home field advantage. You're an outsider. And you're only there for a 4 weeks -1 month - you don't know the EMR and how to order stuff or do stuff (discharge, admit, place consults). You don't even know where the bathrooms are. And you don't know the residents there, the nurses there, etc. And yet you're suppose to "stand out". You're no longer a student - you're a resident. And they expect you to function as a resident. It's a whole different level of expectations (why do you think July/August intern year is so hard?)
TL;DR: It's hard. It's possible - plenty of DO do it every year. But you need a game plan and you need to bring your best game. Planning on getting an academic IM residency is a start. It's a marathon, not a sprint.
Just my perspective as someone who did an academic residency and fellowship, and participated in the interviews and ranking of potential residents/fellows.
