The timetables reflect extended journey times due to trains slowing down as a safety precaution when the temperature is expected to reach 36 degrees or above.
The timetables will be in effect until at least Friday January 17 and will apply to Traralgon, Bairnsdale, Seymour, Shepparton, Albury, Swan Hill, Echuca, Ararat, Maryborough, Geelong and Warrnambool trains.
All of these lines, except Traralgon, Bairnsdale, Geelong and Warrnambool, operated to the heat timetable today (Monday).
Ballarat and Bendigo line trains are being replaced with coaches as the Regional Rail Link works continue.
V/Line chief executive Theo Taifalos said heat-related changes generally apply to trains departing between noon and 8pm.
"We know it's going to be a busy week for travel with Melbourne hosting Big Bash Cricket, A-League Soccer and the Australian Open tennis championships," Mr Taifalos said.
"Extra coaches, carriages and trains have been added to services where possible. However our message to customers is to plan ahead and allow additional travel time. If you can catch an earlier train or coach, please do that so that you get to Melbourne in plenty of time for your event."
"Heat timetables reflect increased journey times for trains that are typically restricted to a maximum speed of 90km/h. This is for safety reasons because the heat can cause steel tracks to expand and even buckle."
V/Line is supporting trains with coaches throughout the heat timetable to ensure customers can get to where they need to go if there are issues with air conditioning on some older train sets.
Customers can keep informed by: Following V/Line on Twitter
Downloading the My Line app
Registering for SMS notifications
Calling on 1800 800 007
Downloading the heat timetable at vline.com.au
Customers are advised to bring bottled water (trains have drinking water onboard) and to delay travel if feeling unwell.
To cater for expected demand for travel to and from sporting events, the following lines will have additional services today.
V/Line will have standby coaches at Southern Cross to supplement trains on any line as required. Ballarat: Additional coaches have been organised for services leaving in the late afternoon to Melbourne. A return special coach service to Ballarat will leave Southern Cross at 11.15pm.