Chullin 111a: Perhaps the reason it was allowed to cook the heart and liver was because they dipped them in boiling water, so that the blood was cooked inside the meat and was thus unable to come out. This is similar to the story of Rav Huna, who ate unsalted meat dipped in vinegar, and Rav Nachman, who ate unsalted meat dipped in boiling water.
חולין קיא ע”א אי נמי מיחלט הוה חליט ליה מעיקרא כי הא דרב הונא חלטי ליה בחלא ורב נחמן חלטי ליה ברותחין. וכתב הרי”ף שהגאונים גזרו על זה כיון דאין אנו בקיאין. והערוך השולחן בסימן ס”ט סקס”ח ביאר החשש של הגאונים ואח”כ כתב ומ”מ דעה ראשונה עיקר להלכה ולכן לצורך מותר.
Rabbi Moshe Feinstein was asked by his grandson, Rabbi Mordechai Tendler, how to prepare meat for a person with a heart condition and high blood pressure, whose doctor told him to avoid salt. R’ Moshe said, “There are two ways: the first is to have a separate pot, cut the meat up into small pieces and drop them into vigorously boiling water. Although we don’t usually use this as a method of kashering meat, because the Gaonim say we are not expert in using it, in this case one can be lenient.
“The second way is to use another type of salt, such as ammonium chloride or potassium chloride. The question about this is only whether such salt works to remove blood. If it is a naturally occurring salt, it definitely works. For we see that Sodom salt has different components from our salt, since it causes blindness, yet it works for kashering. But if it does not occur naturally, then we don’t know if it removes blood.”
Rabbi Tendler suggested that the person should do both: first salt with another type of salt, and then drop into boiling water. This way, if the salt doesn’t work, there is at least a chance that the boiling will work. Reb Moshe said perhaps, but one need not do both. He concluded that the first idea would be the best one to use.
Source: Mesores Moshe, v. 1, p. 209