If you are a European Union (EU) Citizen, you can use the National Health services (public hospitals) by showing a valid European Health Insurance Card. You will be charged the same fee as a Portuguese citizen.
If you are a Non-European Union (Non EU) Citizen, valid International Insurance is necessary. You should check with the service provider which Health units you can use during your stay. However, as a norm, you should always check what coverage your national health insurance provider gives you.