We see in this text of the Mishna that the Meiri does not quote the heart at all.

Rav Moshe Schreiber, known as the Chatam Sofer, was born in 1763 in Frankfurt, Germany and died in Pressburg in 1840. While the Neo-Orthodox sought to engage the maskilim (enlighteners) and to directly combat them, the Chatam Sofer adopted the view of “Chadash assur min HaTorah” – all that is novel in religious practice is forbidden by the Torah. Since this response (# 338) states that irreversible cessation of heart beat is one sign of death, those who do not accept BSD as halachic death quote this response as proof that a beating heart, at least according to the Chatam Sofer, is a sign of life and thus a person who is BSD and on a respirator is not dead according to halacha. Those that accept BSD as halachic death point out that a) in the very same response he states that cessation of respiration is the classical definition of death according to Jewish law and to understand this apparent contradiction they point out b) this teshuva was written as a challenge and response to the secular law instituted by the Duke of Mecklenberg, Germany, in 1772 that one must wait 3 days before burying a corpse in order to ensure the person is truly dead. According to this reading, the Chatam Sofer is simply stating the natural order of death in those days (before the invention of a respirator) is unconsciousness, irreversible cessation of heart beat, and then irreversible cessation of respiration. He states Jewish law only requires irreversible cessation of respiration as the determinant of death, but if the secular authorities want to wait even longer they can wait until cessation of heart beat and then bury the person without waiting 3 days.

Rav Tzvi Hirsch ben Yaakov Ashkenazi, also known as the Chacham Tzvi, was born in 1660 and died in 1718(His son was Rav Yaakov Emden). This response states that a beating heart is a requirement for life. But clearly the Chacham Tzvi was not talking about a case of brain death where the person (or chicken as in this case) can’t breathe. Those who claim that brain-stem death is not halachic death, quote this responsa to support their position because it put emphasis on the heart. But those who accept BSD as halachic death point out that while the Chacham Tzvi writes one needs a beating heart to live, and it necessary for life, he does not write that a beating heart alone is sufficient in and of itself. When he writes the “soul is in the heart” it is rhetorical flourish to indicate that without a beating heart a person or animal can’t live. But again, that is not say it is sufficient for human life. A analogy would be that an airplane needs an engine to fly and to be called an airplane. But that does not mean if you have a working engine that you have an airplane.

Mishna states that is a living organism is decapitated, even though limbs are moving it is dead according to Halacha.