What is the ruling on the prayer of one who has prayed on a chair for more than three months due to a heart surgery?

The scholars have unanimously agreed on the permissibility for a sick person to pray while sitting if he is unable to stand during an obligatory prayer, and he will receive the full, undiminished reward. They based this on the Hadith: "If a servant falls ill or travels, what he used to do when he was healthy and resident will be written for him." Inability to stand is not a prerequisite for being excused; rather, evident difficulty or fear of increased illness permits sitting, such as the case of patients who have undergone heart surgeries.