I have had 3 chickens die of a heat attack.

[u/AgeLow6160]

I have a small free range flock and I have had 3 die of a heat attack. I have seen 2 of them have it . It came on sudden. They didn't look well so I put them separately. I saw two of them start breathing heavily then pass with in minutes. Did they eat something . What can I do to help the rest of the flock .