For example, men having heart attacks are more likely to present with the classic chest pain radiating to their arm. Women can have chest pain, but often present as sudden onset of nausea and vomiting with no pain. That's a rare presentation of a heart attack in a man, so a man complaining of severe nausea is more likely to be thought of as GI in nature, but if you know he's trans then alarm bells start screaming that this might be cardiac and you need to do an EKG now.

This is why we need more medical research focused on trans and intersex bodies. It's honestly a travesty that it hasn't been studied much, largely due to the pushback from oppressive governments and transphobes. The problem extends beyond trans people, so much medical research is modeled on white cis male bodies, but I'm sure you're already aware of that issue.

Transition affects nearly every part of the body. It's already known that trans brains more closely resemble their cis counterparts rather than their sex assigned at birth (citations: NIH.gov, Scientific American). It wouldn't make sense to treat a trans woman as a cis man for brain imaging. In trans men, testosterone deepens the vocal chords and can even slow down or stop periods. In trans women, estrogen shrinks the prostate and can even reverse male pattern baldness. Surely there are other effects on internal medicine, both positive and negative

Part of trans liberation involves sponsoring more research in this topic. In your heart attack example, has it been scientifically proven that the symptoms are immutable with transition? Does the amount of time someone's been transitioning affect it? These are genuine questions, I don't know the answers to them