The Cart Viewed event will fire when a user clicks on the bag or view bag. This can be accessed multiple ways:

When the user is in the PDP and adds to cart
When the user clicks on the bag or cart icon and the cart opens
When the user clicks the option that takes them to the cart

The Event Properties unique to the Cart Viewed event include:

"event_properties": {
    "event_id": "D43336A0-74AC-484B-A54F-834C16C95777",
    "cart_view_source": "icon",
    "cart_view_source_id": null,
    "cart_view_source_title": null,
    "multi_currency_code": "USD",
    "cart_total_items": "3",
    "cart_total_items_list": ["Shirt", "Jogger", "Sweatpants"],
    "cart_total_product_id_list": ["7152220719679", "7206462221695", "2226467043391"],
    "total_discount_amount": "0.0",
    "cart_subtotal": "170.95",
    "cart_total": "170.95",
    "cart_discounted_items_list": [],
    "cart_id": "4431220719679"
  }

event_id String : The unique identifier of the session associated with the event. This event will also exist on the Event object level as well

cart_view_source String : The screen, page, or distinct portion of the app in which the Cart Viewed was fired

Note: The various types can be referenced in the Note: Event Sources and types page

cart_view_source_id String : The distinct product id of the product that triggered the Cart Viewed event. The field will only populate if the source of the Cart Viewed is related to a product page

cart_view_source_title String : The distinct product title of the product that triggered the Cart Viewed event. The field will only populate if the source of the Cart Viewed is related to a product page

multi_currency_code String : The current currency the user has selected in the app

cart_total_items Integer : The total count of current items in the cart after the cart i[dated

cart_total_items_list List : A list of all of the product titles (represented as strings) in the cart after the cart updated

cart_total_product_ids_list List : A list of all of the product id's (represented as strings) in the cart after the cart updated

total_discount_amount Float : The amount that was taken off the checkout from the discount code(s) applied

cart_subtotal Float : The value of the cart before any discounts or gift cards are applied

cart_total Float : The value of the cart after any discounts or gift cards are applied

cart_discounted_items_list List : A list of all of the product titles (represented as strings) that are discounted in the cart

cart_id String : The Shopify identifier for the current cart state. This identifier changes when a certain cart state expires