The deadly Zika virus, which is already known to cause birth defects and a neurological condition that can lead to paralysis, may have serious adverse effects on the heart, says a study.

In a study of a small group of adult patients with Zika and no previous history of cardiovascular disease, all but one developed a heart rhythm problem and two-thirds had evidence of heart failure, the researchers said.

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"We know that other mosquito-borne diseases, such as dengue fever and chikungunya virus, can affect the heart, so we thought we might see the same with Zika. But we were surprised by the severity, even in this small number of patients," said the study's lead author Karina Gonzalez Carta, cardiologist and research fellow at Mayo Clinic in the US.

The findings are scheduled to be presented at the American College of Cardiology's 66th Annual Scientific Session on March 18 in d in Washington, DC.

The nine patients (six were female, and mean age was 47) were seen at the Institute of Tropical Medicine in Caracas, Venezuela, within two weeks of having Zika-type symptoms. 

They reported symptoms of heart problems, most commonly palpitations followed by shortness of breath and fatigue. 

Only one patient had any previous cardiovascular problems (high blood pressure), and tests confirmed that all of the patients had active Zika infection. 

Patients underwent an initial electrocardiogram (EKG), a test that shows the electrical activity of the heart, and in eight of the patients, the EKG suggested heartbeat rate or rhythm concerns. 

These findings prompted further examination which showed serious arrhythmias (improper beating of the heart) in eight patients and heart failure in six cases. 

The patients have been followed since July 2016, and none of their cardiac issues have resolved, but symptoms have improved following treatment for heart failure or atrial fibrillation, Carta said.

It is known that Zika can cause microcephaly, a severe birth defect in babies born to women infected with the virus, and Guillain-Barré syndrome, a neurological condition that can lead to muscle weakness and, in severe cases, paralysis.

"Following this research, we want patients who are suffering from Zika symptoms also to be aware of the cardiac symptoms because they might not connect the two," Carta said.