How to motivate a co-founder that is starting to lose interest?

Apart from a heart to heart talk, what else could one do to keep motivating their co-founders to be most productive and not lose interest in the vision?

I would think it is time for a come to Jesus conversation, gauge level of interest and if they aren't on the same page as you, it's time to cut loose. If you let this fester, it's going to result in resentment and it will eventually unwind, do it now (if needed) in a congenial way vs. combative.

I have been in this exact situation, and in my opinion no matter what you do, its going to be a constant uphill battle. In my case I pushed too hard and ended up losing not only my co-founder but also a friend. My honest advice would be to sit down, and openly and frankly discuss the reasons for him/her losing interest and motivation to continue. If there are things discussed that you are going to work on as a partnership or as individuals to make it work, then do them and set a meeting in advance when you will sit down and evaluate if they have been done and more importantly if they have made a difference. Perhaps start discussing buy out options, or change of roles within the company. Understand that for as long as the two of you aren't on the same page, your businesses performance is ultimately going to suffer. So you need to sort it out ASAP.

It sounds as though they need to reconnect with their and the company's values. I would sit them down and discuss why you set your business up together and what you hoped to achieve, then look at and really appreciate how far you've both come since then. I would then ask them, if you're sitting there together 3 years from now, what do they want to have achieved/have happened in the business for them to be happy? You may need to create or modify a strategy to provide meaning to that vision, but align it with company goals and your goals too, and hopefully they will have a renewed sense of purpose.

This article is really good: blog.strategiccoach.com/magic-vision/

I agree with the others.

I'd probably take a conversation with the co-founder to find out whether he or she really wants it as bad as you do. I believe in the ability to motivate, but you should motivate your employees, not the head of the company; and even not the co-founder. If he does not want it bad, he should not be on it.