An 80-year-old man stabbed his wife to death after she promised to have sex with him at Christmas day but changed her mind and refused after he took Viagra.

Italian man, Vito Cangini has been accused of killing his wife, Natalia Kyrychok, 61, because she refused to have sex with him after he took a Viagra pill while at home in Fanano di Gradara, eastern Italy, on December 25.

Viagra pills, which are usually blue in colour, are taken orally to treat erectile dysfunction.

Kyrychok’s refusal prompted a furious fight, during which Cangini, who was almost 20 years older than his wife, accused her of being attracted to her boss hence her refusal to have sex with him.

Cangini then allegedly stabbed her to death, leaving his wife’s bloodied body on the floor. After the crime he then went to bed.

The following morning, he reportedly ate breakfast, walked his dog and came back home as if nothing tragic had happened.

In the afternoon, he reportedly took his dog for another walk before he phoned the restaurant where his wife had worked as a chef for two years and told the owner he would never see her again.

‘I know there was something going on between you two,’ Cangini reportedly told the restaurant boss his wife worked for.

The restaurant owner then called the police, who visited the suspect’s home.

When officer reached the home they found Ms Kyrychok’s body with at least four stab wounds including one to the heart.

Cangini was taken into custody and the suspected murder weapon was found at the crime scene.

The investigation continues .