Breast Implants with my Pectus Carinatum deformity. Will I get a nice cleavage? Is it true the implants will drift to the sides?

Kuddos to your surgeon for telling you the truth! Breast implants have a tendency to drift down and out despite most chest malformations. Women need to understand that breast implants are heavy and will drift towards gravity's pull. This means down and out (down when standing and out when lying down). This will happen regardless of technique used - gravity always wins. Now, the pull of gravity is less if the implant is small=less weight. So, if you are dead set in increasing volume to your breasts do so with the smallest implant possible. Implants cause a variety of risks and complications needing maintenance at some point. Examples are: skin stretch deformities, irreversible muscle and surrounding tissue damage, nipple numbness, chronic pain, capsular contractures, infection, etc. For more information on the risks and complications associated with breast implants you can visit the breast implant revision forum on this site. Do your research. This is a good start!Best wishes and kind regards,

Thank you for the question. Careful breast implant pocket dissection and careful selection of breast implant size/profile will be necessary to address your concerns about the space between the breasts. Of course, there may be some anatomic limitations as to how closely the breast implants can be placed, without risking breast implant malposition complications. Remember (when it comes to breast implant pocket dissection and achievement of ideal breast implant cleavage) that each nipple/areola complex must be centered on each breast mound.
Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you're looking for. Ask to see lots of examples of his/her work.  
2. Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "C or D cup" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate. The use of computer imaging may be very helpful during this communication phase.
3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery. The use of temporary intraoperative sizers, viewing the patient's breasts in the upright and supine position, are very helpful during the breast implant selection process.
I hope this, and the attached link, helps.

You should know that it is mostly the bra that gives you cleavage, not the breasts. The breast size and volume helps of course. With you pectus carinatum deformity your chest wall shape will likely contribute to the position of your implants. Since this is an outward protruding deformity, the implants will likely be displaced laterally when you lie down. This is simply due to gravity and your shape. It is very likely that your breasts already do that now when you lie down. Overall, this is not a contraindication to breast augmentation.