NATO cannot possibly be one of the "heads" in this prophecy.
THE PROPHECY
And I stood upon the sand of the sea, and saw a beast rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy... And I saw one of his heads as it were wounded to death; and his deadly wound was healed: and all the world wondered after the beast. (Rev 3:3,12)
THE INTERPRETATION
And here is the mind which hath wisdom. The seven heads are seven mountains, on which the woman sitteth. And there are seven kings: five are fallen, and one is, and the other is not yet come; and when he cometh, he must continue a short space. And the beast that was, and is not, even he is the eighth, and is of the seven, and goeth into perdition. And the ten horns which thou sawest are ten kings, which have received no kingdom as yet; but receive power as kings one hour with the beast. These have one mind, and shall give their power and strength unto the beast. (Rev 17:9-13)
We know that the Beast of Revelation 13 is none other than the Antichrist, the Man of Sin, the Son of Perdition, and the Little Horn revealed by Daniel. Evidently he will have ten nations and ten heads of state as his allies. And he will sit in the temple of God in Jerusalem and will blaspheme God and Christ.
It has long been held that those ten nations are related to the former Roman Empire, and will more than likely be ten nations within the European union. Since the "woman" who rides on the Beast has been identified my many as the Catholic church, it would seem that these nations were a part of the Holy Roman Empire. Those major nations were Germany, Czech Republic, Slovenia, Austria, Croatia, Belgium, and the Netherlands as well as large parts of modern Poland, France and Italy. "Wounded to death" probably means the total destruction of one of those nations and then its being rebuilt. Almost all these nations are in the process of self-destruction right now but we would be unwise to identify which one will be completely destroyed. Since NATO is simply a military alliance, it cannot be regarded as either a nation or a head of state.