Hyperdactyly (or polydactyly) is the presence of extra fingers and/or toes or both and occurs in about 1 out of every 500 births in humans. Given that 130 million humans are born every year, that means lots of occurrences. Francesco A. Lentini was born with three legs. Being born with extra limbs is rare, but has occurred frequently enough that it has a name: Polymelia.
this article tells us
Cor triatriatum is a rare congenital cardiac anomaly, in which a fibromuscular membrane divides the atrium in two. It was first reported in 1868.6 Cor triatriatum, a heart with 3 atria (triatrial heart), is a congenital anomaly in which the left atrium (cor triatriatum sinistrum) or right atrium (cor triatriatum dextrum) is divided into 2 parts by a fold of tissue, a membrane, or a fibromuscular band.
Note that these birth defects (maybe events is a better word) are sporadic, i. e., they are not inherited from parents but are due to a random mutation. Also, interestingly, Octopuses have 3 hearts and 9 brains.
So it seems that nature cares little for what you find delusional or that would drive you bonkers. Stupid nature.
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