SHANGHAI, June 27 -- THE number of patients diagnosed with heart attacks has increased by more than 30 percent now that the weather in Shanghai is wet and sultry.

Local hospitals such as Ruijin and Renji have received more myocardial infarction cases than usual every day and doctors say the condition was triggered by the humid and sweltering weather of the Plum Rain season, Shanghai Morning Post reported today.

"The wet and hot weather can easily make people feel suffocated and they get agitated," Lu Ankang, the director of the outpatient department of Ruijin Hospital told the newspaper.

Those who are usually healthy may neglect their health during the season and hesitate to see doctors, which can cause sudden heart attacks and even death, Lu said.

Lu suggested that a 30-minute nap during lunch time was helpful to reduce the risk of myocardial infarction by 30 percent while people should also rest well at night and try to relax at work.

Those with a history of heart problems need to pay special attention to their health from 4am to 10am every day, a peak period for heart attacks and which is called "devil time" by doctors, Lu said.

This year's plum season, started on June 21, is expected to last at least one month, according to Shanghai Meteorological Bureau. The season occurs when plums mature each year and is always marked by frequent heavy rainfalls and muggy weather.