In Act V Scene 3 of Macbeth, Macbeth's state of mind and heart (i.e., regrets) can only be implied by what he says about the witches oracle or to Seyton and the servant or to the Doctor who is there to attend to Lady Macbeth. The most common reading of Macbeth Act V Scene 3 is that Macbeth is blustering in confidence in the belief that the witches have promised him invincibility.
The witches Oracle stated that he had no need of fear until a man not born of woman challenged him and the Birnam forest moved to Dunsinnae. These are both physical impossibilities. Therefore, it is as good as saying Macbeth need never have fear. So this reading interprets everything Macbeth says to his servant, to Seyton, to the Doctor and about "physique" as the arrogant, confident commanding of a king. So by this reading, Macbeth has no regrets except the one regret that his wife has broken and is mentally deranged. He says to the Doctor:
...find her disease,
And purge it to a sound and pristine health,
I would applaud thee to the very echo,
That should applaud again.
Another, less common, reading of the same scene is that Macbeth is ranting in hysteria and is, in his own fashion, as mad as Lady Macbeth. He starts out the scene by commanding that no more reports be brought to him; he does this because all reports contradict what the witches told him. This is significant because he followed what the witches told him in regard to Duncan and there were deeper ramifications than he was prepared for. Therefore, his faith in the witches is shaken. Yet, having come this far, their oracle is all he has to hold onto. In this reading, Macbeth is like a drowning man who is holding onto a shattered branch.
His next statement is a repetition of the witches oracle pertaining to Malcolm and the Birnam forest. Macbeth's long protracted explanation of their sayings followed by launching into a diatribe about his servants cheek color may attest to the unhinged, hysterical condition of Macbeth's own mind. In this case, it can be inferred that Macbeth regrets everything from anger at Duncan's decision, to listening to the witches, to being overpowered by his wife's allusions to broken promises, to the foul act against Duncan.
In Act 5 Scene 3, Macbeth starts out by regretting the way his life has turned out in a genericbut vivid manner. In Line 24:
"My way of life
Is fall'n into the sere, the yellow leaf,.."
The choice of the word 'fall'n" definitely signifies regret or some kind of failure. The metaphorical use of 'the yellow leaf ' indicates a downward turn of events that can only usher in death literal or figurative as in the fallen yellow leaves of the autumn season.
Macbeth also regrets that at this point, he cannot and will not age gracefully. He knows what the most important qualities of a happy, health old age are per Line 27:
' As honor, love, obedience, troops of friends,'
Per line 28, he knows that these that these qualities will not be available to him. He knows with with deep almost embittered regret what is in store for him as in Line 29:
'Curses not loud but deep, mouth-honor breath,'
His choice of words as he describe the 'Curses...' is quite significant. In 'not loud but deep, mouth-honor, breath,..", the description of the 'Curses' is so vivid that the audience can almost feel their impact which is definitely regrettable. The regrets climaxes and comes out with cutting clarity in Line 30:
'Which the poor heart would fain deny, and dare not.'
Use of term 'poor heart' signifies pure regret of past events and 'fain deny' his desire to deny the regrettable events. He still has enough presence of mind, however, to admit that much as he would like to, he cannot deny the past any more than he can erase it