Toddler died from pneumonia, heart disease

Pneumonia and heart disease contributed to a toddler's death in NSW's Hunter Valley, preliminary autopsy results have shown.

The 19-month-old boy was found unconscious at a home in Cessnock on Wednesday morning.

When paramedics arrived, CPR was being administered as the boy had gone into cardiac arrest.

After further attempts to restart his heart, he was taken to Cessnock Hospital in a critical condition where he later died.

Preliminary autopsy results show pneumonia and cardiomyopathy - a disease of the heart muscle - among a range of factors that contributed to the boy's death.

The autopsy did not show a conclusive cause of death and further testing is being carried out.

Maitland Detective Inspector John Zdrilic said police would wait for the full autopsy results to decide if there were any suspicious circumstances.

"Anytime that a 19-month-old dies, it's tragic, and for the sake of everybody we are looking at the circumstances," Insp Zdrilic told AAP.