"The heart did not lie about what it saw." This is read in two ways: with the doubling (tashdid) and with the light pronunciation (takhfif). The one who reads it with doubling says: "The heart of Muhammad did not deem false what it saw," meaning: in the kingdom of Allah and His signs. And the one who reads it with the light pronunciation says: "The heart of Muhammad did not lie about what it saw," meaning: it confirmed the vision and affirmed it.
﴿مَا كَذَبَ الْفُؤَادُ مَا رَأَى﴾ وَهِي تقْرَأ على وَجْهَيْن: بالتثقيل وَالتَّخْفِيف، من قَرَأَهَا بالتثقيل يَقُول: مَا كذّب فؤاد محمدٍ مَا رأى؛ أَي: فِي ملكوت اللَّه وآياته، وَمَنْ قَرَأَهَا بِالتَّخْفِيفِ يَقُولُ: مَا كذّب فؤاد محمدٍ مَا رأى؛ أَي: قد صدق الرُّؤْيَة فأثبتها.