Dr Rungsrit Kanjanavanit, a cardiologist at Chiang Mai University's Maharaj Hospital, said the number of patients suffering acute myocardial infarction dramatically increases at this time of the year - notorious for farm burn-offs and thick smog across the North.
The amount of tiny-particle dust now exceeds safe levels in Lamphun, Chiang Mai and Lampang provinces, while flights in Mae Hong Son were cancelled due to poor visibility.
"From my observation at this hospital, heart attack cases have risen from three to four a month to three to four a day. This phenomenon that happens every dry season and has been continuing for more than 6 years now," Rungsrit said.
He indicated that air pollution could increase the chance of heart attack, especially when the volume of particulate matter with a maximum diameter of 2.5 microns (PM2.5) is high.
"Unlike PM10, which is larger particulate matter in the air, PM2.5 can be inhaled into the pulmonary alveolus inside the lungs, which thickens blood and sometime blocks the blood vessels," he explained.
"Everyone should stay indoors; especially vulnerable persons including children, the elderly and those who have a heart condition, high blood pressure or diabetes, if the air pollution is high. They should relocate if possible," he said.
The doctor suggested people should check air quality in their area daily via the "Air4Thai' application, available in both iOS and Android smartphones.
At Mae Hong Son, airport director Weerawat Takong said Karn Air's ART-60 flights to and from Chiang Mai have been cancelled due to poor visibility since Monday. Pilots require visibility of at least five kilometres but visibility is now only three kilometres. Local officials have been spraying water into the air to lower the dust level.
Officials were also doing this in Lampang. Nakhon Lampang Mayor Thanin Supasang started an air pollution reduction campaign, with fire trucks spraying water into the air.
During the dry season from January to March, farmers often burn their fields to grow new crops - despite officials urging them not to.