So... The current occupier of the Oval Office is eyeing a new unproven treatment for Covid-19 promoted to him by Ben Carson (Housing and Urban Development Secretary, former neurosurgeon, and dude who thinks the pyramids were used to store grain) and the My Pillow Guy (the My Pillow Guy (seriously, this guy has no qualifications to take him seriously on this topic.))
There is research on the BioRxiv preprint server that reports;
...we found that prophylactic oleandrin administration at 30 concentrations down to 0.05 µg/ml exhibited potent antiviral activity against SARS-CoV-2Prophylactic and Therapeutic Inhibition of In Vitro SARS-CoV-2 Replication by Oleandrin - Plante, et al.
NOTE: Research published on a preprint server has not yet been through peer-review.
But let's look at the basics from just this statement. The volume of 0.05 µg/ml is 50ng/ml. With this being a prophylactic, as I understand how this works, it will need to be present everywhere, which means it needs to be in the blood. That's likely lethal for the majority of people. Less than half that amount has been proven fatal.
This would give a total fatal blood concentration of cardiac glycosides of about ∼20 ng/ml in the deceased blood.A fatal case of oleandrin poisoning - Ibrahim A. Wasfi, et al
Wikipedia has a reasonable page on Oleandrin too.