An explanation of the second hadith in the Heart Therapy Series:
The Messenger salla Allahi alayhi wa sallam said: (The qalb [heart] was given this name only because of its fluctuations. The heart is like a feather in the wilderness—at a base of a tree—that continues to be turned on its head by the wind) reported by Ahmad and al-Tabarani. Al-Iraqi declared it to be hasan, and al-Albani declared it as sahih.
قال رسول الله صلى الله عليه وسلم: (إِنَّما سُمِيّ القَلْبَ مِن تَقَلُّبِهِ إنَّما مَثلُ القلبِ مَثلُ ريشَةٍ بالفَلاةِ تَعَلَّقَتْ في أَصْلِ شَجَرَةٍ يُقَلِّبُها الرِّيحُ ظَهْراً لِبَطْنٍ)
رواه أحمد والطبراني وحسنه العراقي (تخريج أحاديث الإحياء) وصححه الألباني (صحيح الجامع 2365)