The heatwave will affect prices of soft commodities such as grains, livestock etc. Farmers are going to suffer irrigation issues, drought, livestock mortality etc. and this will cause the price of these commodities to increase.
Stock prices of EU companies will also be affected negatively because some workers will not be able to work due to the heat.
Stocks of energy companies in the EU will also fall because they may have to shut down some of their plants which pump in river water to cool them. If the river water is too hot, the machinery will not be able to cool down.