Five Maltese aged between 22 and 39 were arrested during a police raid in Triq is-Serkin, Marsa today.
They were found in possession of more than a kilo of heroin probably intended for trafficking.
The police said some were found in a shed which caught fire.
Animals which were locked in the shed with the culprits were saved through the intervention of the police and members of the Civil Protection Department.
They included horses, ducks and birds.
Those arrested hail from Birkirkara, Marsa, Cospicua and Ħamrun. They are being held by the police to assist them in their investigations.
The police said they are expected to be arraigned in the coming days charged with involvement in trafficking and aggravated possession of heroin, breaching bail conditions and animal cruelty.
An inquiry is being held.