Are there cons to using one business card for more than one of your businesses?

Personally, I think it depends on the businesses. For instance, I've had a client who was a fitness trainer but also sold nutritional products. We ended up doing one side of their business card with the fitness training and another with the nutritional products. Since both of the things kind of went hand in hand, it made more sense. If you have two (or more) very disparate businesses, it's usually better to market them separately. This is especially true if each business reaches different markets.

Id tell you to never mix the brands, as it sends a very mixed message to your audience. There are better experts than me on this site related to branding and marketing, but that's my two cents on the subject.

One con would be to cause the potential client to wonder, how focused and committed to their business you would be if it appeared you had many fingers in many pies. Sowing a seed of doubt in their mind might not be in your best interest.

I agree that you can combine brands if they enhance each other, however, this needs to be done carefully so it does not create undue confusion for the person receiving the card. Business cards are not terribly expensive, my advice would be to keep things separate.

I would say "Definitely" - Your company's brand is ultimately its "personality". You want your brand to inspire certain emotions, stand for certain values and connect with clients on a personal level.
Each company has its own brand, so having multiple brands on one card is going to have the same emotional effect as meeting someone with multiple personality disorder...
Just don't do it.

I work for a company that is committed to growth and Uses the Action name in many contexts. The Business cards are different on each side one side is for Action Staffing Services, the other side is for Action Bartending School. I think that the card shows commitment to success.

I agree with Sherry... if the business are close in offerings it could work to have both on one card... but, if they are significantly different then I could be confusing... and with the price of business cards these days being so low there's no reason really not to print another set.

If the card represents a parent company or an ownership group it makes sense. Otherwise I'm not sure it does...
If the companies are so closely tied and share clients, they should probably be amalgamated into one bigger, stronger brand. There will be other marketing, advertising and accounting benefits to be reaped in doing so. HOWEVER, if you have strategically identified and implemented distinct and separate brands for a reason, then combining them on a card must undermine that objective. So if they are better off with their own identities, make two cards.

If the businesses enhance each other or go well together then this might work, but totally different businesses and the prospective client may think Jack of all trades - master of none.

I agree with many of the answers already given but I wonder if they have actually answered your question. You asked about business "brands". Does this mean that you have a parent company that represents several products? If that is the case, your parent company branding should definitely be prominently displayed with the other brands displayed in smaller icons. This is of course, assuming that you play the same role for all products.