You can add Marketo buttons to your Salesforce Layouts. Here’s an example:
Click Setup. Search for “search layout” and click the Search Layouts under Leads.
Click Edit in the Leads List View row.
Add Add to Marketo Campaign, Send Marketo Email, and Add to Watch List buttons to the Selected Buttons and Save.
Press and hold the Shift key to select all three buttons at once.
Repeat these steps for your Contacts (all three buttons) and Accounts (only one button: Add to Watch List).
You cannot add Marketo buttons to Opportunities.