You are facing the problem of differentiating between _strong_, _weak_, and _mixed_ declension of adjectives. I will illustrate the three forms with the adjective _kalt_ and the plural noun _Venen_ in accusative case.


### _Strong_ declension ###

The form _kalte_, which you think was correct, is called _strong_ declension. It appears when there is no article or other word declined like an adjective:

> _kalte_ Venen

In your example, however, the strong declension does not work, because the pronoun _meine_ is also declined like an adjective.


### _Weak_ declension ###

The _weak_ declension appears in connection with a definite article:

> die _kalten_ Venen


### _Mixed_ declension ###

Finally, when there is yet another adjective, or a word that is declined like an adjective (such as _meine_), then _mixed_ declension is used:

> _meine_ _kalten_ Venen

This is actually the form in your example.