Infant sleep patterns are one of the most common sources of concern for parents. While there is a wide range of products and information claiming to support infant sleep, available to parents, the empirical evidence supporting these can be varied. This study aims to investigate the effectiveness of a heart-beating, breathing doll (Lulla Doll) on infant sleep. Five infants aged between 4 and 8 months and their parents (who wished to use the doll) were recruited through social media. The participants were followed, in a multiple-baseline across participants design through 3 phases, baseline, intervention and follow up. Infant sleep was tracked through the use of prospective parent reported sleep diaries and objective videosomnography (VSM) recordings of sleep states. Two families chose to employ a behavioural intervention following the use of the doll and data collection continued in these cases. Results of the study showed no clear effect of the doll on infant sleep, either in parental diary recordings or in VSM sleep states. The behavioural intervention was effective in reducing the number of night wakings, and duration of night wakings for one participant as well as changing her VSM sleep states. These changes in sleep state organisation included an increase in the number of active to quiet sleep transitions before wake, longest sleep period and sleep efficiency and a decrease in wake duration. Behavioural intervention resulted only in changes in sleep onset delay for the other participant. Results are discussed in the light of this finding and suggest future directions which may contribute further to the understanding of the effect of environmental stimuli on infant sleep.