A German court has sentenced a male nurse to life in prison for killing patients with cardiovascular medication.

The 38-year-old nurse identified only as Niels H. was convicted of two counts of murder and attempted murder.

Niels H. had been injecting dangerous doses of cardiovascular medications to his patients, so he can perform - as he described it - his excellent resuscitation skills.

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The defendant apologized to the victims' families last week saying he acted on impulse.

Niels H., whose full name is withheld under German privacy laws, worked at the intensive care unit of the Delmenhorst Clinic in Delmenhorst, Germany from 2003 to 2005. 

The prosecutors said 174 patients died during Niels H.'s shifts.

Based on the investigation, the death rate in the Delmenhorst clinic nearly doubled during Niels H.'s stint there and the use of heart medication jumped dramatically.

A psychiatric expert had told the court Niels H. admitted causing the deaths of 30 patients. At least 60 others survived.

Other senior doctors, who earlier testified during his trial, said Niels H. was often present when patients were being resuscitated. 

He was described as a "passionate medic" and made good relationships with clinic staff.

Niels H. was previously tried in 2008 for attempted murder charges after a colleague discovered he was overdosing his patient. 

He was convicted and sentenced to seven and a half years in prison. 

But the high number of deaths while he was working at the clinic prompted the police to investigate more. 

It was only then that authorities realized the gravity of his crimes.

Niels H. was originally charged with three murders. 

However, the court found him guilty on two counts.  The court explained prosecution failed to prove he was behind the third death.

Tagsneils h., delmenhorst, Germany, overdose