The FAA's website, in its list of medical conditions disqualifying for a would-be pilot, includes a number of cardiac conditions and procedures that would not intuitively seem, on their own, to warrant keeping someone on the ground, and, yet, automatically disqualify the applicant (even if they are completely asymptomatic or the condition has been corrected) from receiving a standard-issue medical certificate, requiring them to beg the FAA for a special-issuance certificate ([italicised brackets] indicate my additions):
[...]
Cardiac valve replacement [even if far in the past, with no history of symptoms or complications, and even if it completely and permanently corrected the precipitating condition]
Coronary heart disease that has been treated [even if completely resolved by said treatment] ...
...
Heart replacement [even with no history of complications]
Myocardial infarction [even if far in the past and devoid of complications or any recurrence]
Permanent cardiac pacemaker [even if causing no complications and completely resolving the underlying pacemaker-necessitating condition]
[...]
Even if some of these conditions have the potential to be associated with other, potentially-impairing conditions (such as cardiac arrhythmiae, heart failure, or heart transplant rejection), those associated conditions, if present, would be perfectly visible in their own right, without the need for using the conditions in the aboveexcerpted list as proxies. In addition, some of the above procedures (such as valve replacement, pacemaker implantation, and some types of coronary-artery-disease interventions) are curative, or functionally-curative, procedures, and, yet, automatically disqualify their recipients from receiving a standard-issue medical certificate.
Why is this?