Hundreds of thousands of New Zealanders are unknowingly living with a silent killer. High blood pressure, also known as hypertension, is the single biggest risk factor behind heart disease, which is the leading cause of death in the country. The condition contributes to nearly half of all cardiovascular deaths, meaning about 4000 lives are lost each year. Heart Foundation medical director Dr Gerry Devlin said one in three adults over 30 had the condition, yet only 25% had it under control. “High blood pressure damages your arteries and can lead to heart attack and stroke,” Dr Devlin said. “It rarely has symptoms, which is why so many people don’t realise they have it.” There are about 350,000 people living with the undiagnosed condition, but managing it can dramatically reduce the risk of a medical emergency and protect cardiovascular health. “For every 10-point drop in your systolic blood pressure, you reduce your risk of a heart event by 20%.…